Add note on spec

docs/blueql/1.overview.md

@@ -18,7 +18,10 @@ Just like SQL, BlueQL has three categories of commands/queries inside it:
 
 Jump to [differences from SQL](#differences-from-sql).
 
-## Language specification
+## Informal language specification
+
+Note that this is not a formal specification! It's intended for developers and users looking to *use* Skytable. If you're someone who is designed in the actual formal specification (for example, a proper grammar definition) please raise an issue and we'll get it done. Since no users have actually requested for it, it has
+not been worked on.
 
 ### Identifiers
 Can begin with any ASCII alphabet or an underscore (`_`) and then have any number of alphanumeric characters and/or underscores.