Add tutorials guidelines in the main tutorials branch

[luisaFelixSalles]

Change the contributing section:

• Updates on the main page
• Add section specific for the documentation
• Add guidelines to write tutorials

The contributing section is organized as :

.
├── Contributing
│   ├── Documentation
│   │    ├── Tutorials guidelines
│   ├── Develop code

Preview on how it renders

Contributing section main page

Documentation sub section

Tutorials guidelines

Develop code sub section

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.44%. Comparing base (627c2de) to head (3ae2f67).

Additional details and impacted files

@@                      Coverage Diff                      @@
##           doc/new-tutorials-section    #1950      +/-   ##
=============================================================
- Coverage                      88.50%   88.44%   -0.07%     
=============================================================
  Files                             89       89              
  Lines                          10251    10251              
=============================================================
- Hits                            9073     9066       -7     
- Misses                          1178     1185       +7     

[PProfizi]

Remark for later: redirect to the PyAnsys guidelines in the Develop code section.