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-RootCache.md

@@ -0,0 +1,37 @@
+---
+layout: default
+title: Plugin RootCache
+---
+
+This plugin caches your buildroots. It creates archive of your buildroot and puts it in `config_opts['plugin_conf']['root_cache_opts']['dir']`, which is be default `/var/cache/mock/NAME_OF_CHROOT/root_cache/cache.tar.gz`. It is enabled by default.
+
+
+## Configuration
+
+This plugin is enabled by default and has the following values built-in:
+```python
+config_opts['plugin_conf']['root_cache_enable'] = True
+config_opts['plugin_conf']['root_cache_opts'] = {}
+config_opts['plugin_conf']['root_cache_opts']['age_check'] = True
+config_opts['plugin_conf']['root_cache_opts']['max_age_days'] = 15
+config_opts['plugin_conf']['root_cache_opts']['dir'] = "%(cache_topdir)s/%(root)s/root_cache/"
+config_opts['plugin_conf']['root_cache_opts']['compress_program'] = "pigz"
+config_opts['plugin_conf']['root_cache_opts']['extension'] = ".gz"
+config_opts['plugin_conf']['root_cache_opts']['exclude_dirs'] = ["./proc", \
+   "./sys", "./dev", "./tmp/ccache", "./var/cache/yum" ]
+```
+
+* `age_check` - if set to `True` (which is default), then cache date is checked. See option `max_age_days` bellow. Additionally if some config is newer than cache file, then the cache is invalidated as well.
+* `max_age_days` - if `age_check` is `True` and cache is older than this value, the cache is invalidated.
+* `dir` - where to put cached files.
+* `compress_program` - which compress program to use. By default `pigz` is used. If not present, then `gzip` is used.
+* `extension` - the cache file is always named as `cache.tar$extension`. When you use different compress program e.g. `bzip2`, you should set different extension e.g. `".bz2"`.
+* `exclude_dirs` - list of directories, which should not be archived.
+
+**WARNING:** You should disable `root_cache` plugin when using `lvm_root` plugin - having two caches with the same contents would just slow you down.
+
+**NOTE:** If you have enough disk storage you can speed-up it a bit by disabling archiving of cache:
+```python
+config_opts['plugin_conf']['root_cache_opts']['compress_program'] = ""
+config_opts['plugin_conf']['root_cache_opts']['extension'] = ""
+```