Add README

Description was copied from the initial #206 PR comment by @kaniblu.

D2Coding/README.rst

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+D2Coding for Powerline
+======================
+
+:Font creator: Naver (company)
+:Source: https://github.com/naver/d2codingfont
+:Patched by: `Kang Min Yoo <https://github.com/kaniblu>`_
+
+D2Coding is a monospace font developed by a Korean IT Company called Naver. Font 
+is good for displaying both Korean characters and latin characters, as sometimes 
+these two languages could share some similar strokes.