Update to use an external invite-bot for slack

Author: amithkk

source/getting-help.rst

@@ -1,4 +1,4 @@
 Getting Help
 ============
 
-If you need any help with the DBoM Open Source Project, have ideas for a use case or have any related queries, head on over to our `Slack Workspace <http://dbom-project.slack.com/>`__
+If you need any help with the DBoM Open Source Project, have ideas for a use case or have any related queries, head on over to our `Slack Workspace <https://communityinviter.com/apps/dbom-project/join-the-dbom-slack/>`__