Update Heroku Deploy Doc to Reflect Requirements for Socket Mode

[raycharius]

Summary

When deploying an app with Socket Mode to Heroku, the Procfile needs to have contents of:

worker: node {{app}}

Spent some time figuring it out yesterday, maybe this will help others save that time 😄

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #932 (7c4cb0a) into main (118019d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #932   +/-   ##
=======================================
  Coverage   66.22%   66.22%           
=======================================
  Files          13       13           
  Lines        1205     1205           
  Branches      355      355           
=======================================
  Hits          798      798           
  Misses        338      338           
  Partials       69       69           

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[seratch]

Thanks! Looks great to me 👍