Added short gpg-agent plugin description.

Plugins.md

@@ -1,4 +1,3 @@
-
 Enable the plugins you want by editing your _~/.zshrc_ file. Example:
 
     plugins=(rails3 git ruby)
@@ -147,6 +146,12 @@ Clean apt cache
 
 **Maintainer:** [robbyrussell](https://github.com/robbyrussell)
 
+## gpg-agent
+
+* gpg-agent - starts gpg-agent (with ssh support) if not running and includes its environment variables
+
+**Maintainer:** [fwalch](https://github.com/fwalch)
+
 ## git
 
 * git - adds a lot of git aliases ( g*x* e.g. gd - git diff) and functions for pulling for dealing with the current branch