add known issue in readme

sql_export/README.rst

@@ -9,6 +9,21 @@ There are some restrictions in the sql sql request, you can only read datas.
 No update, deletion or creation are possible.
 A new menu named Export is created.
 
+Known issues / Roadmap
+======================
+
+Some words are prohibeted and can't be used is the query in anyways, even in a select query :
+
+* delete
+* drop
+* insert
+* alter
+* truncate
+* execute
+* create
+* update
+
+
 Bug Tracker
 ===========