Update doc with cardinality warning

instrumentation/opentelemetry-instrumentation-sqlalchemy/src/opentelemetry/instrumentation/sqlalchemy/__init__.py

@@ -86,6 +86,8 @@
     Invoking engine.execute("select * from auth_users") will lead to sql query "select * from auth_users" but when SQLCommenter and attribute_commenter is enabled
     the query will get appended with some configurable tags like "select * from auth_users /*tag=value*/;" for both server query and `db.statement` span attribute.
 
+Warning: capture of sqlcomment in ``db.statement`` or ``db.query.text`` may have high cardinality without platform normalization. See `Semantic Conventions for database spans <https://opentelemetry.io/docs/specs/semconv/database/database-spans/#generating-a-summary-of-the-query-text>`_ for more information.
+
 
 Usage
 -----