Doc event bolt python

[pdontha]

Fixed minor bugs for the syntax and event dict object in the examples.

Category (place an x in each of the [ ])

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• [ x] Document pages under /docs
• Others

Requirements (place an x in each [ ])

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

• 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.
• I've run ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

Merging #220 (7e240f0) into main (01894d7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #220   +/-   ##
=======================================
  Coverage   91.63%   91.63%           
=======================================
  Files         159      159           
  Lines        4769     4769           
=======================================
  Hits         4370     4370           
  Misses        399      399           

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[mwbrooks]

Thanks @pdontha for helping to improve our documentation! I've previewed this update locally and it renders okay. LGTM