README: added basic description

Author: jirikuncar

README.rst

@@ -0,0 +1,46 @@
+DirSON
+======
+
+Encode and decode JSON files as directory structure in Git.
+
+Installation
+------------
+
+Clone this repository and run pip:
+
+.. code-block:: console
+
+   $ pip install -e .
+
+Move to a repository where you would like to filter JSON files and
+add following lines to files:
+
+``.git/config``
+
+.. code-block::
+
+   [filter "dirson"]
+       smudge = "dirson smudge"
+       clean = "dirson clean"
+       required
+
+``.gitattributes``
+
+.. code-block::
+
+   \*.json  filter=dirson
+
+
+Pointer file format
+-------------------
+
+Git DirSON's pointer file looks like this:
+
+.. code-block::
+
+   version https://raw.githubusercontent.com/jirikuncar/dirson/v1/spec
+   oid sha1:2f769492d6b634b86b82e916630da8a693e9c20e
+   size 12345
+
+It tracks the version of Git DirJSON you're using, followed by a unique identifier
+for the JSON file (oid). It also stores the size of the target JSON file.