docs: change project name & write a better README

[hadrien]

Problem

• Project name is too long
• README is not surfacing the appeal of the project

Solution

• Use a shorter name: Fastapi-Async-SQLA -> FastSQLA
• Add a first list of features
• Write a better example in the readme

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (264a29e) to head (6f4e3c5).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #10   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines           93        93           
  Branches         6         6           
=========================================
  Hits            93        93           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.