README: Clarify strict mode

The strict mode may not be confused with the server-side strict mode
set via the sql_mode system variable.
Fixes #376

Author: julienschmidt

Diff for: README.md

@@ -263,7 +263,9 @@ Valid Values:   true, false
 Default:        false
 ```
 
-`strict=true` enables the strict mode in which MySQL warnings are treated as errors.
+`strict=true` enables a driver-side strict mode in which MySQL warnings are treated as errors. This mode should not be used in production as it may lead to data corruption in certain situations.
+
+A server-side strict mode, which is safe for production use, can be set via the [`sql_mode`](https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html) system variable.
 
 By default MySQL also treats notes as warnings. Use [`sql_notes=false`](http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_sql_notes) to ignore notes. See the [examples](#examples) for an DSN example.