Issue #3311001 by phenaproxima: Document the fixtures used by StagedProjectsValidatorTest

tests/fixtures/StagedProjectsValidatorTest/README.md

...ive/modules/dev-test_module/dev-test_module.info.yml.hide

...dded/active/modules/test_module/test_module.info.yml.hide

...t/new_project_added/active/vendor/composer/installed.json

...st/new_project_added/active/vendor/composer/installed.php

...ged/modules/dev-test_module/dev-test_module.info.yml.hide

...d/modules/dev-test_module2/dev-test_module2.info.yml.hide

...dded/staged/modules/test_module/test_module.info.yml.hide

...ed/staged/modules/test_module2/test_module2.info.yml.hide

...t/new_project_added/staged/vendor/composer/installed.json

...st/new_project_added/staged/vendor/composer/installed.php

...datorTest/no_errors/active/vendor/composer/installed.json

...datorTest/no_errors/staged/vendor/composer/installed.json

...idatorTest/no_errors/staged/vendor/composer/installed.php

...est/project_removed/active/vendor/composer/installed.json

...est/project_removed/staged/vendor/composer/installed.json

...est/version_changed/active/vendor/composer/installed.json

...est/version_changed/staged/vendor/composer/installed.json

...ject_staged_validation/no_core_requirements/composer.json

...ation/no_core_requirements/vendor/composer/installed.json