Create link.md

link to --link docs from README to separate docs entry

Author: ashumz

docs/link.md

@@ -0,0 +1,8 @@
+### code-server --link
+Run code-server with the beta flag `--link` and you'll get TLS, authentication, and a dedicated URL 
+for accessing your IDE out of the box.
+
+```bash
+$ code-server --link
+Proxying code-server, you can access your IDE at https://example.cdr.co
+```