Merge the installation instructions into the index

Author: AA-Turner

docs/index.rst

@@ -8,7 +8,6 @@
 .. toctree::
    :maxdepth: 2
 
-   install
    usage
    extend
    sample
@@ -18,6 +17,23 @@
    contrib
 
 
+Installation
+------------
+
+This extension is tested on python 2.7 and 3.3+.
+
+The package is available in the Python Package Index::
+
+    pip install sphinx-argparse
+
+And also in conda-forge::
+
+    mamba -c conda-forge install sphinx-argparse
+
+Enable the extension in your sphinx config::
+
+    extensions += ['sphinxarg.ext']
+
 
 References
 ==========