Changes after renaming qlxad to quantlib-xad

[auto-differentiation-dev]

Description

This PR has some minor documentation changes after the qlxad integration module repository has been renamed to quantlib-xad

[github-actions[bot]]

Test Results

       29 files  ±0         29 suites  ±0   12m 32s :stopwatch: -27s   1 218 tests ±0    1 218 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0  35 322 runs  ±0  35 322 :heavy_check_mark: ±0  0 :zzz: ±0  0 :x: ±0 

Results for commit 33f7c1dd. ± Comparison against base commit 86f65016.

:recycle: This comment has been updated with latest results.

[coveralls]

coverage: 97.954%. remained the same when pulling 33f7c1dda69590dbc2ef6ddadd3fcfa79fa5067b on feature/rename-qlxad into 86f65016a4c23f920b5355785176d633e7b47a8a on main.