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-BuildrootLock.md

@@ -0,0 +1,48 @@
+---
+layout: default
+title: Plugin buildroot_lock
+---
+
+buildroot_lock Plugin
+=====================
+
+This plugin generates an additional build artifact—the buildroot *lockfile*
+(`buildroot_lock.json` file in the result directory).
+
+The *lockfile* describes both the list of buildroot sources (e.g., a list of
+installed RPMs, bootstrap image info, etc.) and a set of Mock configuration
+options.  Using this information, Mock can later reproduce the buildroot
+preparation (see the [Hermetic Builds feature page](feature-hermetic-builds)).
+
+This plugin is **disabled** by default but is automatically enabled with the
+`--calculate-build-dependencies` option.  You can enable it (for all builds) by
+this configuration snippet:
+
+```python
+config_opts['plugin_conf']['buildroot_lock_enable'] = True
+```
+
+**Note:** This plugin does not work with the `--offline` option.
+
+
+Format of the *buildroot_lock.json* file
+----------------------------------------
+
+The file `buildroot_lock.json` is a JSON file.  List of JSON Schema files is
+installed together with the Mock RPM package:
+
+    rpm -ql mock | grep schema
+    /usr/share/doc/mock/buildroot-lock-schema-1.0.0.json
+    /usr/share/doc/mock/buildroot-lock-schema-1.1.0.json
+
+Currently, we do not provide a compatibility promise.  Only the exact same
+version of Mock that produced the file is guaranteed to read and process it.
+For more information, see [Hermetic Builds](feature-hermetic-builds).
+
+Also, in the future we plan to switch to a standardized tooling so we operate
+with a standardized format, too.  For more info see the [DNF5 feature
+request][discussion], [rpm-lockfile-prototype][] and [libpkgmanifest][].
+
+[discussion]: https://github.com/rpm-software-management/dnf5/issues/833
+[rpm-lockfile-prototype]: https://github.com/konflux-ci/rpm-lockfile-prototype
+[libpkgmanifest]: https://github.com/rpm-software-management/libpkgmanifest