docs: Add get_signup_redirect_url docstring

# Submitting Pull Requests

## General

 - [ ] Make sure you use [semantic commit messages](https://seesparkbox.com/foundry/semantic_commit_messages).
       Examples: `"fix(google): Fixed foobar bug"`, `"feat(accounts): Added foobar feature"`.
 - [ ] All Python code must formatted using Black, and clean from pep8 and isort issues.
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 - [ ] If your changes are significant, please update `ChangeLog.rst`.
 - [ ] If your change is substantial, feel free to add yourself to `AUTHORS`.

 ## Provider Specifics

 In case you add a new provider:

- [ ] Make sure unit tests are available.
- [ ] Add an entry of your provider in `test_settings.py::INSTALLED_APPS` and `docs/installation.rst::INSTALLED_APPS`.
- [ ] Add documentation to `docs/providers/<provider name>.rst` and `docs/providers/index.rst` Provider Specifics toctree.
- [ ] Add an entry to the list of supported providers over at `docs/overview.rst`.

Just adding some comments to help with documentation generation.

Reviewed-on: https://codeberg.org/allauth/django-allauth/pulls/4202
Co-authored-by: devo-wm <[email protected]>
Co-committed-by: devo-wm <[email protected]>

allauth/account/adapter.py

@@ -200,6 +200,9 @@ def send_mail(self, template_prefix: str, email: str, context: dict) -> None:
         msg.send()
 
     def get_signup_redirect_url(self, request):
+        """
+        Returns the default URL to redirect to directly after signing up.
+        """
         return resolve_url(app_settings.SIGNUP_REDIRECT_URL)
 
     def get_login_redirect_url(self, request):