Added documentation for converter CLI

[germa89]

Close #1785

[germa89]

@PipKat whenever you can :)

You might also wants to have a look at the docstrings of:

• convert_script: https://github.com/pyansys/pymapdl/blob/e1d3e9a7cb937a78199ea27f494c62b2e635e89b/src/ansys/mapdl/core/convert.py#L89-L188
• convert_apdl_block: https://github.com/pyansys/pymapdl/blob/e1d3e9a7cb937a78199ea27f494c62b2e635e89b/src/ansys/mapdl/core/convert.py#L236-L321
• cli: https://github.com/pyansys/pymapdl/blob/e1d3e9a7cb937a78199ea27f494c62b2e635e89b/src/ansys/mapdl/core/convert.py#L1087-L1114

And the help arguments of these lines:
https://github.com/pyansys/pymapdl/blob/e1d3e9a7cb937a78199ea27f494c62b2e635e89b/src/ansys/mapdl/core/convert.py#L1014-L1069

You might need a different PR for these :)

[codecov]

Codecov Report

Merging #1789 (8521c1b) into main (e1d3e9a) will increase coverage by 81.78%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           main    #1789       +/-   ##
=========================================
+ Coverage      0   81.78%   +81.78%     
=========================================
  Files         0       44       +44     
  Lines         0     7709     +7709     
=========================================
+ Hits          0     6305     +6305     
- Misses        0     1404     +1404     

[PipKat]

@germa89 Most edits were to follow the Google style guide.

[germa89]

Thank you @PipKat for your comments. Very useful!!