docs(quickstart): add basic usage section

why: Provide getting-started examples beyond installation.
what:
- Add Commands section with git init/clone/status examples
- Add Subcommand Managers section with branches/tags/remotes
- Link to full API reference

Author: tony

docs/quickstart.md

@@ -52,3 +52,49 @@ via trunk (can break easily):
 
 [pip]: https://pip.pypa.io/en/stable/
 [uv]: https://docs.astral.sh/uv/
+
+## Basic Usage
+
+### Commands
+
+Run git commands directly using {class}`~libvcs.cmd.git.Git`:
+
+```python
+from libvcs.cmd.git import Git
+
+git = Git(path='/path/to/repo')
+
+# Initialize a new repository
+git.init()
+
+# Clone a repository
+git.clone(url='https://github.com/vcs-python/libvcs.git')
+
+# Check status
+git.status()
+```
+
+### Subcommand Managers
+
+Work with branches, tags, remotes, and more using the Manager/Cmd pattern:
+
+```python
+from libvcs.cmd.git import Git
+
+git = Git(path='/path/to/repo')
+
+# List and filter branches
+branches = git.branches.ls()
+remote_branches = git.branches.ls(remotes=True)
+
+# Create and manage tags
+git.tags.create(name='v1.0.0', message='Release 1.0')
+tag = git.tags.get(tag_name='v1.0.0')
+
+# Work with remotes
+remotes = git.remotes.ls()
+origin = git.remotes.get(remote_name='origin')
+origin.prune()
+```
+
+See {doc}`/cmd/git/index` for the full API reference.