extension/index: rst to md

Change-Id: I735b4aea8e3c28681c3a752ae2e8613600daa179

extension/index.rst → extension/index.md

-################
-Extension manual
-################
+# Extension manual
 
 The Jami extension manual is a reference for Jami extension developers, documenting the various aspects of the Jami Extension API and architecture.
 In September 2020, the Jami team added extensions as a call feature for GNU/Linux, Windows, macOS, and Android users.
 This enables personalized call and chat experiences by using available extensions.
 Additionally, anyone is also able to transform awesome ideas into brand new Jami extensions!
 
-**NOTE: Jami source code also uses the term “plugin” to refer to “extension”.**
+```{important}
+Jami source code also uses the term “plugin” to refer to “extension”.
+```
 
-.. toctree::
-   :maxdepth: 1
+```{toctree}
+:maxdepth: 1
 
-   how-it-works
-   how-to-build
-   how-to-publish
-   creating-jami-extensions
-   jami-extension-certificate
-   extension-store-jami-client
-   tensorflow-extension
+how-it-works
+how-to-build
+how-to-publish
+creating-jami-extensions
+jami-extension-certificate
+extension-store-jami-client
+tensorflow-extension
+```
\ No newline at end of file