Link to github app in .env for slugEnv

Finding the link to the app on GitHub to edit the settings (like adding a `redirect_uri`) is hard. Having the link right where the app is defined means most users will not have to read the docs from #1359.

packages/keystatic/src/api/api-node.ts

@@ -70,7 +70,7 @@ export async function handleGitHubAppCreation(
 KEYSTATIC_GITHUB_CLIENT_ID=${ghAppDataResult.client_id}
 KEYSTATIC_GITHUB_CLIENT_SECRET=${ghAppDataResult.client_secret}
 KEYSTATIC_SECRET=${randomBytes(40).toString('hex')}
-${slugEnvVarName ? `${slugEnvVarName}=${ghAppDataResult.slug}\n` : ''}`;
+${slugEnvVarName ? `${slugEnvVarName}=${ghAppDataResult.slug} # https://github.com/apps/${ghAppDataResult.slug}\n` : ''}`;
 
   let prevEnv: string | undefined;
   try {