Latiosu feat/docker (#5572)

* Add dockerised local development environment

* Enable tini (--init) for server container

See https://docs.docker.com/compose/compose-file/#init for details

* Add local development environment documentation

* Add a tip for how-to connect a client on the same machine

* Add specialized tools/docker folder

Co-authored-by: Eric <latiosworks@gmail.com>

.github/CONTRIBUTING.md

@@ -7,6 +7,7 @@ Table of Contents
   * [Reporting Bugs](#reporting-bugs)
   * [Suggesting Enhancements](#suggesting-enhancements)
   * [Issue Labels](#issue-labels)
+  * [Local Development Environment](#local-development-environment)
   * [Become a Team Member](#become-a-team-member)
 
 Reporting Bugs
@@ -161,6 +162,13 @@ For the most part you as a user will have no reason to worry about the **Milesto
 [search-rathena-label-typemaintenance]: https://github.com/rathena/rathena/issues?q=is%3Aissue+is%3Aopen+label%3Atype%3Amaintenance
 [search-rathena-label-typequestion]: https://github.com/rathena/rathena/issues?q=is%3Aissue+is%3Aopen+label%3Atype%3Aquestion
 
+Local Development Environment
+-----------------------------
+
+Developers can get up and running quickly with a Dockerized development environment that installs all dependencies needed to run and develop on rAthena.
+See tools/docker/README.md for details
+
+
 Become a Team Member
 --------------------