Guide to org/project structure and forking info

PROJECT_STRUCTURE.md

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+# OpenPGP.js Repositories <!-- omit in toc -->
+
+This documents explains all repositories in the OpenPGP.js organization and how they relate to each other.
+
+**Table of Contents**
+- [Forks](#forks)
+- [Repo Dependency Chart](#repo-dependency-chart)
+
+## Forks
+You will notice a large number of forked projects that are dependencies of OpenPGP.js itself. These are often due to necessary changes that are of no interest to the upstream maintainers, mostly concerning build processes, eg. making node-only libraries available for frontend use. The `tweetnacl` fork is mainly there to shrink the dependency, since most of the library isn’t used.
+
+There’s a [useful discussion](https://github.com/openpgpjs/openpgpjs/discussions/1574) on the topic that includes some analysis of the forks in regard to their upstreams, as well as explainations from the maintainers concerning the reasons for the forks and their versioning.
+
+## Repo Dependency Chart
+
+```mermaid
+flowchart LR
+    CORE -->|depends on| InternalLibraries
+    CORE -->|depends on| PublicLibraries
+    CORE -->|depends on| SoonObsolete
+    CORE .->|will depend on| v6InternalLibraries
+    CORE .->|no longer depends on| UnusedForks
+    subgraph Core
+      CORE(OpenPGP.js)
+    end
+    subgraph NoInternalDependencies [Repos with no internal dependencies]
+      direction LR
+      CLI(sop-openpgp.js)
+      WEBSITE(openpgpjs.org website)
+      GHA(Github Actions fork)
+      HKP-CLIENT(HKP Client)
+      WKD-CLIENT(WKD Client)
+    end
+    subgraph PublicLibraries [Public Libraries]
+      direction LR
+      WEB-STREAMS-POLYFILL(web-streams-polyfill fork)
+      ARGON2ID(Argon2id)
+    end
+    subgraph InternalLibraries [Internal Libraries and Forks]
+      direction LR
+      ASMCRYPTO.JS(openpgp/asmcrypto.js fork)
+      JSDOC(openpgp/jsdoc fork)
+      PAKO(openpgp/pako fork)
+      SEEK-BZIP(openpgp/seek-bzip fork)
+      TWEETNACL(openpgp/tweetnacl fork)
+      WEB-STREAM-TOOLS(openpgp/web-stream-tools) -->|depends on| JSDOC
+    end
+    subgraph v6InternalLibraries [Internal Libraries that will be added in v6]
+      NOBLE-CURVES(Noble Curves fork)
+      NOBLE-HASHES(Noble Hashes fork)
+    end
+    subgraph SoonObsolete [Internal Libraries that will be removed in v6]
+      ELLIPTIC(openpgp/elliptic fork)
+    end
+    subgraph UnusedForks [Unused Forks]
+      direction LR
+      COMPRESSJS(compressjs fork, unused since 2018)
+      ES6-PROMISE(es6-promise fork, seems unused?)
+      EMAIL-ADDRESSES(email-addresses fork, replaced by upstream in 528fbfb, 2019)
+    end
+```