Improve rdonly counter documentation

Author: Kerollmops

Diff for: libraries/liblmdb/mdb.c

@@ -1303,7 +1303,7 @@ struct MDB_txn {
 	MDB_txn		*mt_parent;		/**< parent of a nested txn */
 	/** Nested txn under this txn, set together with flag #MDB_TXN_HAS_CHILD */
 	MDB_txn		*mt_child;
-	/** The count of nested RDONLY txns under this txn */
+	/** The count of nested RDONLY txns under this txn also named child txns */
 	atomic_uint	mt_rdonly_child_count;
 	pgno_t		mt_next_pgno;	/**< next unallocated page */
 #ifdef MDB_VL32