pip: Document --ignore-pkg

pip/readme.md

@@ -45,6 +45,7 @@ You can use that in your manifest like
 * `--cleanup=(scripts|all)`: Add `cleanup` to the manifest. This is used when the packages installed are only used at build time.
 * `--build-only`: Alias to `--cleanup=all`.
 * `--requirements-file=`, `-r`: Reads the list of packages from `requirements.txt` file.
+* `--ignore-pkg=`: Ignore a specific package name in a requirements-file, otherwise ignored.
 * `--checker-data`: This adds `x-checker-data` to modules so you will be notified when new releases happen. See [flatpak-external-data-checker](https://github.com/flathub/flatpak-external-data-checker) for more details.
 * `--runtime=`: Runs `pip` inside of a specific Flatpak runtime instead of on your host. Highly recommended for reproducability and portability. Examples would be `org.freedesktop.Sdk//22.08` or `org.gnome.Sdk/aarch64/43`.
 * `--ignore-errors=`: Allow the generation of empty or otherwise broken files when downloading packages fails.