Add documentation for the chrome.sockets API and manifest key.

chrome/common/extensions/docs/templates/json/manifest.json

 {
   "app": {
     "documentation": "manifest/app.html",
     "example": {},
     "level": "required"
   },
   "app.background": {
     "example": {"scripts": ["background.js"]},
     "level": "required"
   },
@@ skipping 121 matching lines @@
     "example": {}
   },
   "sandbox": {
     "documentation": "manifest/sandbox.html",
     "example": []
   },
   "short_name": {
     "documentation": "manifest/name.html#short_name",
     "example": "Short Name"
   },
+  "sockets": {
+    "documentation": "manifest/sockets.html",
+    "example": {
+      "tcp": { "connect": "*" }, "udp": { "send": "*" }
+    }
+  },
   "storage": {
     "documentation": "manifest/storage.html",
     "example": {
       "managed_schema": "schema.json"
     }
   },
   "theme": {
     "documentation": "themes.html",
     "example": {},
     "level": "only_one"
   },
   "update_url": {
     "documentation": "autoupdate.html",
     "example": "http://path/to/updateInfo.xml"
   },
   "url_handlers": {
     "documentation": "manifest/url_handlers.html",
     "example": {}
   },
   "version": {
     "documentation": "manifest/version.html",
     "example": "versionString",
     "level": "required"
   },
   "web_accessible_resources": {
     "documentation": "manifest/web_accessible_resources.html",
     "example": []
   }
 }