[Docs] Replace recommonmark with MyST parser

We used recommonmark so that we can use markdown in sphinx but it is
buggy and now so switch to better supported MyST-parser.

* Fixed incorrect heading warnings in markdown.
* Added sphinx toctree to markdown using directive as required by MyST.
* Upgraded Sphinx to 4.3

Ref: https://myst-parser.readthedocs.io

1 files changed, 8 insertions, 4 deletions

diff --git a/docs/source/contributing/index.md b/docs/source/contributing/index.md
index afdead24d..8c07a76b1 100644
--- a/docs/source/contributing/index.md
+++ b/docs/source/contributing/index.md
@@ -3,7 +3,11 @@
 Deluge is an open-source project, and relies on its community of users to keep
 getting better.
 
-- [Code contributions](code.md)
-- [Running tests](testing.md)
-- [Documentation contributions](documentation.md)
-- [Translation contributions](translations.md)
+```{toctree}
+:titlesonly:
+
+code
+testing
+documentation
+translations
+```