docs: docs/index to use markdown

Author: tony

docs/index.md

@@ -0,0 +1,33 @@
+(index)=
+
+# tmuxp
+
+## tmux session manager
+
+```{include} ../README.md
+```
+
+```{image} _static/tmuxp-demo.gif
+:width: 100%
+
+```
+
+### Table of Contents
+
+```{toctree}
+:maxdepth: 2
+
+about
+quickstart
+examples
+cli
+plugin_system
+developing
+api
+history
+about_tmux
+glossary
+
+```
+
+