docs: improve readme

[edibotopic]

Attempts to improve the readme by providing:

• a title that includes the product name
• a more concise introductory paragraph that explicitly mentions usage on multiple platforms (e.g., desktop, server)
• a section that clearly outlines briefly the content to be found in the documentation wiki, including SSH authentication

When reading, a user should get a more immediate sense of what the product offers and where more technical information can be found, including information on architecture, etc.

UDENG-4080 UDENG-4083

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.78%. Comparing base (924b003) to head (aaa066b). Report is 2 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #510 +/- ## ========================================== - Coverage 84.84% 84.78% -0.06% ========================================== Files 79 79 Lines 6942 6942 Branches 75 75 ========================================== - Hits 5890 5886 -4 - Misses 736 737 +1 - Partials 316 319 +3 ```

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[edibotopic]

Thanks for these changes. I added a couple of comments though.

Much thanks @jibel . All of your improvements were incorporated in: https://github.com/ubuntu/authd/pull/510/commits/8960da7113502f026339a468bc30337424ee33c8