improve README

see #2

Author: Changaco

README.rst

@@ -1,4 +1,8 @@
-A lightweight Git Large File Storage fetcher written in python
+A lightweight Git Large File Storage fetcher written in python.
+
+This module cannot fully replace the official git-lfs client, it only knows how
+to download the files, cache them (the same way the official client does), and
+place them in a checkout directory. Uploading files is not implemented at all.
 
 Installation
 ============
@@ -10,7 +14,9 @@ python-git-lfs is compatible with python 2 and 3.
 Usage
 =====
 
-::
+Basic: simply run ``python -m git_lfs`` in a normal Git repository.
+
+Advanced::
 
     python -m git_lfs [-h] [-v] [git_repo] [checkout_dir]