Add travis build status to readme.

README.markdown

@@ -3,6 +3,8 @@ ErlyDTL
 
 ErlyDTL compiles Django Template Language to Erlang bytecode.
 
+[![Build Status](https://travis-ci.org/erlydtl/erlydtl.png?branch=master)](https://travis-ci.org/erlydtl/erlydtl)
+
 *Supported tags*: autoescape, block, blocktrans, comment, cycle, extends, filter, firstof, for, if, ifchanged, ifequal, ifnotequal, include, now, regroup, spaceless, ssi, templatetag, trans, verbatim, widthratio, with
 
 _Unsupported tags_: csrf_token, url