[3644] Minor typo corrected.

doc/guide/admin.xml

@@ -35,7 +35,7 @@
       Backend versions are specified in
       a <replaceable>major.minor</replaceable> format. The minor
       number is increased when there are backward compatibile changes
-      introduced.  For example, ithe addition of a new index. It is
+      introduced.  For example, the addition of a new index. It is
       desirable, but not mandatory to to apply such a change; you
       can run on older database version if you want to. (Although, in
       the example given, running without the new index may be at the