Improve release instructions

[mistercrunch]

CATEGORY

Choose one

• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

Improve/clarify the release instructions

[codecov-io]

Codecov Report

Merging #8016 into master will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #8016      +/-   ##
=========================================
+ Coverage   65.58%   65.6%   +0.02%     
=========================================
  Files         469     469              
  Lines       22449   22449              
  Branches     2431    2431              
=========================================
+ Hits        14723   14728       +5     
+ Misses       7606    7601       -5     
  Partials      120     120

Impacted Files	Coverage Δ
superset/db_engine_specs/postgres.py	95.45% <0%> (+22.72%)	⬆️

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[etr2460]

lgtm, thanks for the added docs!