Fix Markdown formatting in a couple of doc files

[Payam Hekmat (phekmat)]

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General Guidelines

• The PR has modified HISTORY.rst with an appropriate description of the change (see Modifying change log).

Command Guidelines

• Each command and parameter has a meaningful description.
• Each new command has a test.

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[Codecov (codecov-io)]

Codecov Report

Merging #2822 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2822   +/-   ##
=======================================
  Coverage   62.89%   62.89%           
=======================================
  Files         480      480           
  Lines       26012    26012           
  Branches     3946     3946           
=======================================
  Hits        16361    16361           
+ Misses       8627     8623    -4     
- Partials     1024     1028    +4

Impacted Files	Coverage Δ
src/azure-cli-core/azure/cli/core/util.py	68.99% <0%> (ø)	⬆️
...-cli-role/azure/cli/command_modules/role/custom.py	19.28% <0%> (ø)	⬆️
...dback/azure/cli/command_modules/feedback/custom.py	34.69% <0%> (ø)	⬆️

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