Added example and documentation for shallowCloneHosts array

See bower/bower#1764 and
bower/bower@26f80d2
for more details

The `shallowCloneHosts` array was not documented up to now.

config.md

@@ -41,6 +41,9 @@ Available configuration variables, in `.bowerrc.` format:
   <a href="#resolvers">"resolvers"</a>: [
     "mercurial-bower-resolver"
   ],
+  <a href="#shallowCloneHosts">"shallowCloneHosts"</a>: [
+    "myGitHost.example.com"
+  ]
 }</code></pre>
 
 ### analytics
@@ -281,3 +284,16 @@ List of [Pluggable Resolvers](http://bower.io/docs/pluggable-resolvers/) to use
   "mercurial-bower-resolver"
 ]
 ```
+
+### shallowCloneHosts
+
+`Array`
+
+Bower's default behavior is to not use _shallow cloning_, since some Git hosts (e.g. older versions of GitHub Enterprise) fail to provide a response when asked to do a shallow clone (with `--depth 1`). This list allows to whitelist hosts that are known to support shallow cloning.
+
+
+```json
+"shallowCloneHosts": [
+  "myGitHost.example.com"
+]
+```