contributions.md Add doc about how to contribute to flatbuffers (#8464)

Author: dbaileychess

docs/README.md

@@ -0,0 +1,23 @@
+# Documentation
+
+This is the source of the FlatBuffers documentation, that is served at
+https://flatbuffers.dev.
+
+
+## Local Building
+
+The documentation can be built and served locally during development, see [https//flatbuffers.dev/contributing/#local-development] for full details.
+
+__tl;dr__
+
+Install:
+
+```
+pip install mkdocs-material
+```
+
+Build and Serve:
+
+```
+mkdocs serve -f docs/mkdocs.yml
+```

docs/mkdocs.yml

@@ -64,3 +64,4 @@ nav:
     - Overview: "schema.md"
     - Evolution: "evolution.md"
     - Grammar: "grammar.md"
+  - Contributing: "contributing.md"

docs/source/contributing.md

@@ -0,0 +1,79 @@
+# Contributing
+
+We encourage community contributions to FlatBuffers through pull requests at the
+main
+[http://github.com/google/flatbuffers](http://github.com/google/flatbuffers)
+repository.
+
+!!! note
+
+    The FlatBuffers project is not staffed by any full time Google employee, and
+    is managed by a small team of 20%ers. So response time and expertise vary.
+
+## Before you contribute
+
+Before we can use your contributions, you __must__ sign one of the following license agreements. The agreements are self-served at the following links.
+
+Our code review process will automatically check if you have signed the CLA, so
+don't fret. Though it may be prudent to check before spending a lot of time on 
+contribution.
+
+### Individual Contributions 
+
+For individuals, the [Google Individual
+Contributor License Agreement
+(CLA)](https://cla.developers.google.com/about/google-individual?csw=1) which is
+self served at the link. The CLA is required since you own the copyright to your
+changes, even after your contribution becomes part of our codebase, so we need
+your permission to use and distribute your code. 
+
+### Corporate Contributions
+
+Contributions made by corporations are covered by the [Google Software Grant and
+Corporate Contributor License
+Agreement](https://cla.developers.google.com/about/google-corporate).
+
+## Code Reviews
+
+All submissions require a code review via Github Pull Requests.
+
+1. Please adhere to the [Google Style Guide](https://google.github.io/styleguide/cppguide.html) for the language(s) you are submitting in.
+2. Keep PRs small and focused. Its good practice and makes it more likely your PR will be approved.
+3. Please add tests if possible.
+4. Include descriptive commit messages and context to the change/issues fixed.
+
+## Documentation
+
+FlatBuffers uses [MkDocs](https://www.mkdocs.org/) to generate the static
+documentation pages served at
+[https://flatbuffers.dev](https://flatbuffers.dev). Specifically, we use the
+[Material for MkDocs](https://squidfunk.github.io/mkdocs-material/) framework.
+
+The documentation source is contained in the main repo under the
+[docs/](https://github.com/google/flatbuffers/tree/master/docs) directory. This
+[automatically](https://github.com/google/flatbuffers/blob/46cc3d6432da17cca7694777dcce12e49dd48387/.github/workflows/docs.yml#L6-L11) get built and published when the commit is made.
+
+### Local Development
+
+We encourage contributors to keep the documentation up-to-date as well, and it
+is easy to with `MkDocs` local building and serving tools.
+
+First install `mkdocs-material` (see
+[Installation](https://squidfunk.github.io/mkdocs-material/getting-started/) for
+other ways)
+
+```
+pip install mkdocs-material
+```
+
+Then, in the `root` directory of flatbuffers, run 
+
+```
+mkdocs serve -f docs/mkdocs.yml
+```
+
+This will continually watch the repo for changes to the documentation and serve
+the rendered pages locally.
+
+Submit your documentation changes with your code changes and they will
+automatically get published when your code is submitted.