[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, 2 insertions, 2 deletions

diff --git a/docs/requirements.txt b/docs/requirements.txt
index c8a0d0546..ff363e0ff 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,4 @@
-sphinx==2.0.*
-recommonmark==0.4.*
+sphinx==4.*
+myst-parser
 sphinx_rtd_theme
 sphinxcontrib-spelling