add-forge-now: Reference the forge type gogs

It's not the same as gitea instances and it's already supported.

swh/web/add_forge_now/templates/add-forge-help.html

@@ -27,6 +27,9 @@ See top-level LICENSE file for more information
           <li>
             <code>gitweb</code>, for <a href="https://git-scm.com/book/en/v2/Git-on-the-Server-GitWeb">gitweb</a> forges
           </li>
+          <li>
+            <code>gogs</code>, for <a href="https://gogs.io/">gogs</a> forges
+          </li>
           <li>
             <code>heptapod</code>, for <a href="https://heptapod.net/">heptapod</a> forges
           </li>

swh/web/add_forge_now/views.py

@@ -84,6 +84,7 @@ FORGE_TYPES: List[str] = [
     "gitlab",
     "gitea",
     "gitweb",
+    "gogs",
     "heptapod",
 ]