Rename master to main in README and other *.md files (#12977)

README.md

@@ -9,9 +9,9 @@
 [![Docs](https://img.shields.io/badge/docs-latest-green.svg)](https://etcd.io/docs)
 [![Godoc](http://img.shields.io/badge/go-documentation-blue.svg?style=flat-square)](https://godoc.org/github.com/etcd-io/etcd)
 [![Releases](https://img.shields.io/github/release/etcd-io/etcd/all.svg?style=flat-square)](https://github.com/etcd-io/etcd/releases)
-[![LICENSE](https://img.shields.io/github/license/etcd-io/etcd.svg?style=flat-square)](https://github.com/etcd-io/etcd/blob/master/LICENSE)
+[![LICENSE](https://img.shields.io/github/license/etcd-io/etcd.svg?style=flat-square)](https://github.com/etcd-io/etcd/blob/main/LICENSE)
 
-**Note**: The `master` branch may be in an *unstable or even broken state* during development. Please use [releases][github-release] instead of the `master` branch in order to get stable binaries.
+**Note**: The `main` branch may be in an *unstable or even broken state* during development. For stable versions, see [releases][github-release].
 
 ![etcd Logo](logos/etcd-horizontal-color.svg)
 
@@ -22,9 +22,9 @@ etcd is a distributed reliable key-value store for the most critical data of a d
 * *Fast*: benchmarked 10,000 writes/sec
 * *Reliable*: properly distributed using Raft
 
-etcd is written in Go and uses the [Raft][raft] consensus algorithm to manage a highly-available replicated log.
+etcd is written in Go and uses the [Raft][] consensus algorithm to manage a highly-available replicated log.
 
-etcd is used [in production by many companies](./ADOPTERS.md), and the development team stands behind it in critical deployment scenarios, where etcd is frequently teamed with applications such as [Kubernetes][k8s], [locksmith][locksmith], [vulcand][vulcand], [Doorman][doorman], and many others. Reliability is further ensured by [**rigorous testing**](https://github.com/etcd-io/etcd/tree/master/tests/functional).
+etcd is used [in production by many companies](./ADOPTERS.md), and the development team stands behind it in critical deployment scenarios, where etcd is frequently teamed with applications such as [Kubernetes][k8s], [locksmith][], [vulcand][], [Doorman][], and many others. Reliability is further ensured by [**rigorous testing**](https://github.com/etcd-io/etcd/tree/main/tests/functional).
 
 See [etcdctl][etcdctl] for a simple command line client.
 
@@ -33,7 +33,7 @@ See [etcdctl][etcdctl] for a simple command line client.
 [doorman]: https://github.com/youtube/doorman
 [locksmith]: https://github.com/coreos/locksmith
 [vulcand]: https://github.com/vulcand/vulcand
-[etcdctl]: https://github.com/etcd-io/etcd/tree/master/etcdctl
+[etcdctl]: https://github.com/etcd-io/etcd/tree/main/etcdctl
 
 ## Community meetings
 
@@ -53,7 +53,7 @@ Time:
 - [May 30th, 2019 11:00 AM video](https://youtu.be/2t1R5NATYG4)
 - [Jul 11th, 2019 11:00 AM video](https://youtu.be/k_FZEipWD6Y)
 - [Jul 25, 2019 11:00 AM video](https://youtu.be/VSUJTACO93I)
-- [Aug 22, 2019 11:00 AM video](https://youtu.be/6IBQ-VxQmuM) 
+- [Aug 22, 2019 11:00 AM video](https://youtu.be/6IBQ-VxQmuM)
 - [Sep 19, 2019 11:00 AM video](https://youtu.be/SqfxU9DhBOc)
 - Nov 14, 2019 11:00 AM
 - Dec 12, 2019 11:00 AM
@@ -84,7 +84,7 @@ The easiest way to get etcd is to use one of the pre-built release binaries whic
 
 For more installation guides, please check out [play.etcd.io](http://play.etcd.io) and [operating etcd](https://etcd.io/docs/latest/op-guide).
 
-For those wanting to try the very latest version, [build the latest version of etcd][dl-build] from the `master` branch. This first needs [*Go*](https://golang.org/) installed ([version 1.16+](/go.mod#L3) is required). All development occurs on `master`, including new features and bug fixes. Bug fixes are first targeted at `master` and subsequently ported to release branches, as described in the [branch management][branch-management] guide.
+For those wanting to try the very latest version, [build the latest version of etcd][dl-build] from the `main` branch. This first needs [*Go*](https://golang.org/) installed ([version 1.16+](/go.mod#L3) is required). All development occurs on `main`, including new features and bug fixes. Bug fixes are first targeted at `main` and subsequently ported to release branches, as described in the [branch management][branch-management] guide.
 
 [github-release]: https://github.com/etcd-io/etcd/releases
 [branch-management]: https://etcd.io/docs/latest/branch_management
@@ -107,7 +107,7 @@ mv /tmp/etcd-download-test/etcd /usr/local/bin/
 etcd
 ```
 
-If etcd is [built from the master branch][dl-build], run it as below:
+If etcd is [built from the main branch][dl-build], run it as below:
 
 ```bash
 ./bin/etcd
@@ -157,15 +157,15 @@ goreman -f ./Procfile.learner start
 
 Now it's time to dig into the full etcd API and other guides.
 
-- Read the full [documentation][fulldoc].
-- Explore the full gRPC [API][api].
+- Read the full [documentation][].
+- Explore the full gRPC [API][].
 - Set up a [multi-machine cluster][clustering].
 - Learn the [config format, env variables and flags][configuration].
 - Find [language bindings and tools][integrations].
 - Use TLS to [secure an etcd cluster][security].
 - [Tune etcd][tuning].
 
-[fulldoc]: https://etcd.io/docs/latest
+[documentation]: https://etcd.io/docs/latest
 [api]: https://etcd.io/docs/latest/learning/api
 [clustering]: https://etcd.io/docs/latest/op-guide/clustering
 [configuration]: https://etcd.io/docs/latest/op-guide/configuration
@@ -202,8 +202,8 @@ See [PR management](https://etcd.io/docs/current/triage/prs/) for guidelines on
 
 These emeritus maintainers dedicated a part of their career to etcd and reviewed code, triaged bugs, and pushed the project forward over a substantial period of time. Their contribution is greatly appreciated.
 
-* Fanmin Shi 
-* Anthony Romano 
+* Fanmin Shi
+* Anthony Romano
 
 ### License