Improve post count documentation

Make clear that the post count only takes into account posts made in the
current forum and doesn't actually count all posts across all forums.

Change-Id: Ia59e16700556d8ede8bf46d514c42dc6d90776b0
diff --git a/docs/op_indicator.md b/docs/op_indicator.md
index 56163d7..8d4cec3 100644
--- a/docs/op_indicator.md
+++ b/docs/op_indicator.md
@@ -20,6 +20,6 @@
 2. The second option makes a request to load the user profile instead of
 searching in the forum the actual threads. This returns the number of posts
 (including new threads, normal replies and recommended replies) made by the user
-over the last year, aggregated by month. The extension sums the values for the
-`n` most recent months (`n` is a configurable value) and then shows this
-resulting number next to the OP's username.
+in the current forum over the last year, aggregated by month. The extension sums
+the values for the `n` most recent months (`n` is a configurable value) and then
+shows this resulting number next to the OP's username.