Improve project documentation

Created MR for the issue and fix some formatting issues according to Readme.md template → format.
Thanks

Eduardo Morales Alberti → made their first commit to this issue’s fork.

I do not really like the commiters that have most of the issues changing the README.txt to README.md.
But I would like to improve the module documentation, so I will to commit some improvements here:

• Now the module appears on the admin/index list, seems like if you do not add it to the menu, it does not appear on the list.
  

• Add menu link on the translation section
  
  
• The hook help was wrong and does not display anything
  
  Before:
  
  
  After (now as in other modules, the help information is extracted from the readme as markdown, that's why I change it here):
  
  

Nice work! Here is some feedback for MR !5

1. The configure option isn't really a configure page as mentioned in #1786994-4: Add a "configure" link directly on "modules" list → , maybe some day if ✨ Add configuration so sites can customize which calls, files, and functions to ignore Needs work is committed?
2. potx.module:28 , two lines earlier, an early return is placed. The Else-statement isn't needed.
3. The description in potx.links.menu.yml is almost the same as the title, maybe something like: 'Get the translation from modules or themes.'?
4. Readme.md: "The potx Drush command provided by the module. Examples:" should be a heading not a list item.
5. I think it would be better to display a summary of the help or a hint to the Drush command feature on the actual potx page and an extended help on the help page. See `path_help()` for an example.