move how_to_contribute page from the wiki to developper documentation

Requirements

• Filling out the template is required. Any Enhancement request that does not include enough information to be reviewed in a timely manner may be closed at the maintainers' discretion.
• All new code requires tests to ensure against regressions

Descriptive title for this enhancement

Rewrite the page https://documentation.fusiondirectory.org/en/how_to_contribute, to help people contribute

Actual behavior

The page is old an unmaintained, the part about translation should go into the developper manual

Expected behavior

Have a link that send to the correct part of the documation on read the docs

Step by step description of new behaviour

1. Write the missing part in the developper documentation
2. Remove old content from the wiki, and link to the developper documentation

Benefits

Have all development, contribution stored in one place

Possible Drawbacks

none

Applicable Issues

development and translations