enhance: Add comprehensive .gitignore for deb-mock project

- Add mock-specific build artifacts (chroot/, mock-*, mockroot/)
- Include package build files (*.deb, *.changes, *.buildinfo)
- Add development tools (.coverage, .pytest_cache, .tox)
- Include system files (.DS_Store, Thumbs.db, ._*)
- Add temporary and backup files (*.tmp, *.bak, *.backup)
- Include local configuration overrides (config.local.yaml, .env.local)
- Add test artifacts and documentation builds
- Comprehensive coverage for Python build system project

This ensures build artifacts, chroot environments, and development
tools are properly ignored in version control.

docs/Plugin-Mount.md

@@ -0,0 +1,50 @@
+---
+layout: default
+title: Plugin Mount
+---
+
+This plugin allows you to mount directories into chroot. The mount plugin is enabled by default, but has no configured directories to mount.
+
+## Configuration
+
+You can disable this plugin by:
+```python
+config_opts['plugin_conf']['mount_enable'] = False
+```
+
+You can configure this plugin by:
+```python
+config_opts['plugin_conf']['mount_enable'] = True
+config_opts['plugin_conf']['mount_opts']['dirs'].append(("/dev/device", "/mount/path/in/chroot/", "vfstype", "mount_options"))
+```
+
+A real life example:
+```python
+config_opts['plugin_conf']['mount_opts']['dirs'].append(("server.example.com:/exports/data", "/mnt/data", "nfs", "rw,hard,intr,nosuid,nodev,noatime,tcp"))
+```
+
+### `/builddir/` cleanup
+
+**WARNING!** The build user's homedir (`/builddir`)  is partially cleaned up even when `--no-clean` is
+specified in order to prevent garbage from previous builds from altering
+successive builds. Mock can be configured to exclude certain files/directories
+from this. Default is `SOURCES` directory to support nosrc rpms:
+
+```python
+config_opts['exclude_from_homedir_cleanup'] = ['build/SOURCES']
+```
+Paths are relative to build user's homedir.
+
+So if you do something like this:
+```python
+config_opts['plugin_conf']['bind_mount_opts']['dirs'].append((os.path.expanduser('~/MyProject'), '/builddir/MyProject' ))
+```
+
+Then you SHOULD do:
+```python
+config_opts['exclude_from_homedir_cleanup'] = ['build/SOURCES', 'MyProject']
+```
+
+otherwise your `~/MyProject` will be wiped out!
+Other option is to not mount it under `/builddir`, but somewhere else (`/opt`, `/mnt`...).
+