[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, 6 insertions, 1 deletions

diff --git a/docs/source/intro/index.md b/docs/source/intro/index.md
index 8342cec1e..ff0f8412e 100644
--- a/docs/source/intro/index.md
+++ b/docs/source/intro/index.md
@@ -3,7 +3,12 @@
 This is a starting point if you are new to Deluge where we will walk
 you through getting up and running with our BitTorrent client.
 
-- [1. Installing Deluge](01-install.md)
+```{toctree}
+:numbered: 1
+:titlesonly:
+
+01-install
+```
 
 <!--
 2. Using Deluge