fix message

.github/workflows/pr_dns.yml

@@ -20,6 +20,7 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               body: `**Welcome**
+                First thing: don't send PR to the master branch, please send to the dev branch instead.
                 Please make sure you've read our [DNS API Dev Guide](../wiki/DNS-API-Dev-Guide) and [DNS-API-Test](../wiki/DNS-API-Test).
                 Then reply on this message, otherwise, your code will not be reviewed or merged.
                 We look forward to reviewing your Pull request shortly ✨