Add to migrations and update docs.

Addresses datamweb#186.

Author: evansharp

docs/install.md

@@ -53,6 +53,8 @@ Therefore, you can add `first_name`, `last_name`, and `avatar` columns to table
 php spark migrate -n Datamweb\ShieldOAuth
 ```
 
+The default size of the `username` field created by Shield is **30** characters. Since Oauth uses the `username` field for the user's email address, this often is not large enough. Consider increasing the size of this field to `VARCHAR(100)`. _The migrations make this change for you_.
+
 > **Note**
 > By default, `Shield OAuth` uses columns named `first_name`, `last_name`, and `avatar`.
 > For any reason, if you want to consider another name for them columns, you can do it through the config file(`config/ShieldOAuthConfig.php`) and set the desired values in:

src/Database/Migrations/2022-10-20-182737_ShieldOAuth.php

@@ -54,6 +54,16 @@ public function up(): void
         ];
 
         $this->forge->addColumn('users', $fields);
+
+        $fields2 = [
+            'username'     => [
+                'type'     => 'VARCHAR(256)',
+                'null'     => true,
+            ]
+        ];
+
+        // use 'modify' since the prerequisite Shield plugin will certainly have created this column
+        $this->forge->modifyColumn('users', $fields2);
     }
 
     public function down(): void