docs: Use markdown index file

Author: tony

docs/index.md

@@ -0,0 +1,21 @@
+(index)=
+
+# libvcs - vcs abstraction layer
+
+```{eval-rst}
+.. include:: ../README.rst
+    :start-line: 3
+```
+
+## Table of contents
+
+```{toctree}
+:maxdepth: 2
+
+api
+developing
+history
+
+```
+
+