Documentation : the wait timeout flag (#188)

* Documentation : the wait timeout flag

I ran into a situation where the timeout was reached at the very beginning of the operations (because I use -D and there was an autovacuum running), and I was confused by the documentation.
The details section of the documentation states clearly that the ACCESS EXCLUSIVE locks are needed at the beginning and at the end of the repack, but I propose to make the `--wait-timeout`flag documentation a little clearer on this.

Thank you for this amazing tool btw !

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Co-authored-by: Andreas Scherbaum <[email protected]>

doc/pg_repack.rst

@@ -197,13 +197,14 @@ Reorg Options
     with the ``--table`` or ``--parent-table`` options.
 
 ``-T SECS``, ``--wait-timeout=SECS``
-    pg_repack needs to take an exclusive lock at the end of the
-    reorganization.  This setting controls how many seconds pg_repack will
-    wait to acquire this lock. If the lock cannot be taken after this duration
-    and ``--no-kill-backend`` option is not specified, pg_repack will forcibly
-    cancel the conflicting queries. If you are using PostgreSQL version 8.4
-    or newer, pg_repack will fall back to using pg_terminate_backend() to
-    disconnect any remaining backends after twice this timeout has passed.
+    pg_repack needs to take one exclusive lock at the beginning and and one
+    exclusive lock at the end of the reorganization. This setting controls
+    how many seconds pg_repack will wait to acquire this lock. If the lock
+    cannot be taken after this duration and ``--no-kill-backend`` option is
+    not specified, pg_repack will forcibly cancel the conflicting queries.
+    If you are using PostgreSQL version 8.4 or newer, pg_repack will fall
+    back to using pg_terminate_backend() to disconnect any remaining
+    backends after twice this timeout has passed.
     The default is 60 seconds.
 
 ``-D``, ``--no-kill-backend``