readme in mysql example

Author: lovasoa

examples/custom form component/README.md

@@ -1,8 +1,12 @@
 # Custom form component
 
-This example shows how to create a simple custom component in handlebars, and use from SQL.
+This example shows how to create a simple custom component in handlebars, and call it from SQL.
 
-It uses MySQL, but does not use any MySQL-specific features, so it should be easy to adapt to other databases.
+It uses MySQL, but it should be easy to adapt to other databases.
+The only MySQL-specific features used here are 
+ - `json_table`, which is supported by MariaDB and MySQL 8.0 and later.
+ - MySQL's `json_merge` function.
+Both [have analogs in other databases](https://sql.datapage.app/blog.sql?post=JSON%20in%20SQL%3A%20A%20Comprehensive%20Guide).
 
 ![screenshot](screenshot.png)