Update Bolt Getting Started for Granular Bot Permissions

[shaydewael]

Summary

A few edits to make the Getting Started guide reflect Granular Bot permissions.

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 #373 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #373   +/-   ##
=======================================
  Coverage   83.03%   83.03%           
=======================================
  Files           7        7           
  Lines         501      501           
  Branches      146      146           
=======================================
  Hits          416      416           
  Misses         56       56           
  Partials       29       29

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[stevengill]

LGTM

[seratch]

@shaydewael 👋 I just sent a pull request to your fork - shaydewael#3
Could you check my PR (of course, no need to review Japanese wordings etc 😅 ) and merge it? Then, we'll be able to merge all the necessary changes here.