Add docs for stats

doc/index.md

@@ -1,4 +1,5 @@
 @include documentation
+@include stats
 @include localization
 @include custom_static
 @include api/api

doc/stats.md

@@ -0,0 +1,18 @@
+# Statistics
+Etherpad keeps track of the goings-on inside the edit machinery. If you'd like to have a look at this, just point your browser to `/stats`.
+
+We currently measure:
+
+ - totalUsers (counter)
+ - connects (meter)
+ - disconnects (meter)
+ - pendingEdits (counter)
+ - edits (timer)
+ - failedChangesets (meter)
+ - httpRequests (timer)
+ - http500 (meter)
+ - memoryUsage (gauge)
+
+Under the hood, we are happy to rely on [measured](https://github.com/felixge/node-measured) for all our metrics needs.
+
+To modify or simply access our stats in your plugin, simply `require('ep_etherpad-lite/stats')` which is a `measured.Collection`.