Explain initial idea

Add a readme file which outlines the initial idea of c-shelve and its use case.

README.md

+This repository is still in the R&D stage.
+
+# What is c-shelve?
+
+`c-shelve` is a command line tool, which can be used to *C*onvert python
+*shelve* archives to use a different backend. Python provides the shelve package to store python object in
+a key-value store, which behaves like a `dict`. Shelve can be used with three different
+backends which mange the archive: `dbm.gdbm`, `dbm.ndbm` or `dbm.dumb`.
+By default, shelve uses `dbm.gdbm`, which is platform dependent. A shelve
+archive created on a `32bit` system can not be opened on a `64bit` system, or
+the other way round, [stackoverflow
+post](https://stackoverflow.com/questions/22645231/shelve-archives-not-openable-on-other-computer).
+
+`c-shelve` is intended to help in this case by converting shelve files to a different
+backend which is platform independent.
+