Add Slack to Footer

[hrittikhere]

Description
Slack is the easiest way for users, contributors and other participants to get going. The Link for Slack is not visible in the footer:

I think we should add that like other projects have done while maintaining the format:

Please let me know what you think about this :) I would love to work on this if this sounds like an appropriate change

[hrittikhere]

Just tried and tested and this should look like something below:

[Sukriti-sood]

Yes, it is the needed addition, as link to slack should be accessible easily.