Add contributing section and move related docs

* Add Contributing nav item / section
* Add Contributing index page as first subitem in the section and
  mention source code and docs repos.
* Move unit test guide, previously under "testing", and style guide
  and doc guide, previously under "more", under "contributing"
  section.

Note:
With Mkdocs a "section cannot have a page assigned to it", hence
the workaround with the first page of the section repeating the section
title (this pattern is also on the mkdocs user docs site -
https://www.mkdocs.org/user-guide/).

An alternative would be to use the section-index plugin:
https://oprypin.github.io/mkdocs-section-index/
It seems quite popular and is likely safe to use (the mkdocs repo
uses a different plugin from the same author).

Signed-off-by: Lukas Puehringer <lukas.puehringer@nyu.edu>

Author: Lukas Puehringer

docs/contribute/README.md

@@ -0,0 +1,13 @@
+# Contributing
+
+The Lind sandbox is developed in the [lind-wasm](https://github.com/Lind-Project/lind-wasm)
+monorepo on GitHub. You can find the documentation assets, including this site,
+in [lind-wasm-docs](https://github.com/Lind-Project/lind-wasm-docs). Please
+contribute to the Lind project by submitting issues or pull requests to these
+repositories.
+
+More detailed guidelines about writing code, tests and documentation are below:
+
+* [Rust Style Guide](styleguide.md)
+* [Unit Tests](unit-tests.md)
+* [Adding to the docs](writeDoc.md)

docs/more/styleguide.md docs/contribute/styleguide.mddocs/more/styleguide.md renamed to docs/contribute/styleguide.md

@@ -24,14 +24,16 @@ nav:
     - Compile Programs: use/compile-programs.md
     - Debug Programs: use/debug-programs.md
     - Run Programs: use/run-programs.md
-  - Testing:
-    - Unit tests: testing/unit-tests.md
+  - Contributing:
+    - contribute/README.md
+    - Rust style guide: contribute/styleguide.md
+    - Unit tests: contribute/unit-tests.md
+    - Adding to the docs: contribute/writeDoc.md
   - More:
     - Maintainers: more/maintainers.md
-    - Adding to the docs: more/writeDoc.md
-    - Style Guide: more/styleguide.md
   - Community: community.md
 
+
   # - Progress: daily.md
   # - WASM Knowledge:
   #   - understandTls.md