docs: move all contrib docs to central source at CONTRIBUTING.md

* remove rarely-used docs/contributing.mdx page and redirect links to
  docs/development/contributing.mdx
* softlink docs/development/contributing.mdx to CONTRIBUTING.md
* add back section of towncrier to CONTRIBUTING.md
* use indirect hyperlinks for all URLs in CONTRIBUTING.md

CONTRIBUTING.md

@@ -36,7 +36,7 @@ prek install
 prek --all-files
 ```
 
-Alternatively, you can use [pre-commit](https://pre-commit.com/):
+Alternatively, you can use [pre-commit][pre-commit]:
 ```bash
 # Requires python
 
@@ -52,6 +52,9 @@ pre-commit run --all-files
 
 These same checks are run in CI via the prek-checks workflow to ensure consistency. These must pass before the PR is merged.
 
+[pre-commit]: https://pre-commit.com/
+[prefligit]: https://github.com/j178/prefligit
+
 ### Running tests locally
 
 Tests, compilation, and linting can be run with standard Cargo commands:
@@ -109,7 +112,7 @@ Alternatively, you can build the documentation using `npm run docs:build` - the
 
 ### Commit Messages
 
-Continuwuity follows the [Conventional Commits](https://www.conventionalcommits.org/) specification for commit messages. This provides a standardized format that makes the commit history more readable and enables automated tools to generate changelogs.
+Continuwuity follows the [Conventional Commits][conventional-commits] specification for commit messages. This provides a standardized format that makes the commit history more readable and enables automated tools to generate changelogs.
 
 The basic structure is:
 
@@ -168,6 +171,7 @@ Contribution by users who violate either of these code of conducts may not have
 their contributions accepted. This includes users who have been banned from
 continuwuity Matrix rooms for Code of Conduct violations.
 
+[conventional-commits]: https://www.conventionalcommits.org/
 [issues]: https://forgejo.ellis.link/continuwuation/continuwuity/issues
 [continuwuity-matrix]: https://matrix.to/#/#continuwuity:continuwuity.org?via=continuwuity.org&via=ellis.link&via=explodie.org&via=matrix.org
 [complement]: https://github.com/matrix-org/complement/
@@ -175,3 +179,32 @@ continuwuity Matrix rooms for Code of Conduct violations.
 [nodejs-download]: https://nodejs.org/en/download
 [rspress]: https://rspress.rs/
 [documentation.yml]: https://forgejo.ellis.link/continuwuation/continuwuity/src/branch/main/.forgejo/workflows/documentation.yml
+
+#### Writing news fragments
+
+In order to make writing our changelogs easier, we make use of [Towncrier]. Towncrier builds changelogs based on
+"news fragments", which are little markdown files in the `changelog.d/` directory that describe individual changes.
+
+When you make a pull request that changes functionality, fixes a bug, or adds documentation, please add a news fragment
+describing your change. The file name *MUST* be in the format of `{pull_request_number}.{type}`, where `{type}` is one
+of the following:
+
+- `feature` - for new features
+- `bugfix` - for bug fixes
+- `doc` - for documentation changes
+- `misc` - for other changes that don't fit the above categories
+
+For example:
+
+```bash
+$ echo "Fixed the quantum flux stabiliser. Contributed by @alice." > changelog.d/42.bugfix
+```
+
+(Note: If you want to credit yourself, you should reference your forgejo handle, however links to other platforms are also acceptable.)
+
+When the next release is made, Towncrier will automatically include your news fragment in the changelog.
+
+You can read more about writing news fragments in the [Towncrier tutorial][tt].
+
+[Towncrier]: https://towncrier.readthedocs.io/
+[tt]: https://towncrier.readthedocs.io/en/stable/tutorial.html#creating-news-fragments