doc(data): support for auto increment (serial) fields

Author: p5quared

src/pages/[platform]/build-a-backend/data/connect-to-existing-data-sources/connect-postgres-mysql-database/index.mdx

@@ -404,6 +404,7 @@ This allows the Amplify team to maintain and enhance the SQL Layer without needi
 | integer            | a.integer()          |
 | bigint             | a.integer()          |
 | tinyint            | a.integer()          |
+| serial*            | a.integer().default() |
 | float              | a.float()        |
 | double             | a.float()        |
 | decimal            | a.float()        |
@@ -429,6 +430,8 @@ This allows the Amplify team to maintain and enhance the SQL Layer without needi
 | json               | a.json()       |
 | enum               | a.enum()          |
 
+*Support for auto increment (serial) fields is limited to PostgreSQL datasources.
+
 ## Troubleshooting
 
 ### Debug Mode

src/pages/[platform]/build-a-backend/data/data-modeling/add-fields/index.mdx

@@ -233,6 +233,9 @@ const schema = a.schema({
   }),
 }).authorization((allow) => allow.publicApiKey());
 ```
+
+If you're working with a Postgres datasource, `.default()` can be used to represent [serial fields](/[platform]/build-a-backend/data/connect-to-existing-data-sources/connect-postgres-mysql-database/#mapping-of-sql-data-types-to-field-types-for-auto-generated-schema).
+
 <Callout>
 **Note:** The `.default(...)` modifier can't be applied to required fields.
 </Callout>