add readme to l theme

themes/l/readme.md

+## l
+
+A theme inspired by [oh-my-zsh](https://github.com/robbyrussell/oh-my-zsh/blob/master/themes/lambda.zsh-theme)'s [lambda](http://zshthem.es/screenshots/lambda.png) theme.
+
+![](http://f.cl.ly/items/2J3M0f2X1j3u471y080I/2.png)
+![](http://f.cl.ly/items/2S25360U1p360E0D2u2g/3.png)
+![](http://f.cl.ly/items/1w0s0Q3x3r2Z1F1l011k/4.png)
+
+
+#### Characteristics
+
+* Current branch
+* Dirty working directory
+* Working directory
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