docs(CHANGES): Add uv installation method for developmental releases

why: Align with vcspull's documentation pattern and provide modern
installation options for users who prefer uv over pip.

what:
- Add uv installation example with --prerelease allow flag
- Maintain existing pip installation instructions
- Remove pipx/uvx/uv tool methods as libvcs is a library, not a CLI tool
- Keep documentation focused on relevant package management tools

refs: Consistent with vcspull's approach to documenting installation methods

Author: tony

CHANGES

@@ -1,14 +1,19 @@
 # Changelog
 
-To install the unreleased libvcs version, see
-[developmental releases](https://libvcs.git-pull.com/quickstart.html#developmental-releases).
+To install the unreleased libvcs version, see [developmental releases](https://libvcs.git-pull.com/quickstart.html#developmental-releases).
 
 [pip](https://pip.pypa.io/en/stable/):
 
 ```console
 $ pip install --user --upgrade --pre libvcs
 ```
 
+[uv](https://docs.astral.sh/uv/):
+
+```console
+$ uv add libvcs --prerelease allow
+```
+
 ## libvcs 0.37.x (unreleased)
 
 <!-- Maintainers, insert changes / features for the next release here -->