Adding README.Debian to explain the basic usage of pre-commit-hooks (Closes: #1093805).

Signed-off-by: Daniel Baumann <daniel@debian.org>

debian/pre-commit-hooks.README.Debian

@@ -0,0 +1,65 @@
+pre-commit-hooks for Debian
+===========================
+
+1. pre-commit
+-------------
+
+pre-commit is a hook framework for the Git version control system. It allows
+managing and maintaining multi-language Git pre-commit hooks.
+
+When using multiple hooks managed by pre-commit, they are usually maintained
+in a Git repository on their own and then included in the pre-commit
+configuration file, within the repository they are being run in, like this:
+
+  --- .pre-commit-config.yaml ---
+  repos:
+  -   repo: https://github.com/pre-commit/pre-commit-hooks
+      rev: v5.0.0
+      hooks:
+      -   id: end-of-file-fixer
+      -   id: trailing-whitespace-fixer
+      -   id: name-tests-test
+  [...]
+  ---
+
+Running 'pre-commit install' and 'pre-commit run --all-files' then will
+automatically download the referenced Git repository (pre-commit-hooks) and
+keep it updated.
+
+A demo repository is available upstream:
+https://github.com/pre-commit/demo-repo
+
+
+2. pre-commit-hooks
+-------------------
+
+As an alternative to referencing a (remote) Git repository and depend on its
+availabilty or the network connectivity to access it, hooks within pre-commit
+can also be configured to be used from the local filesystem. This is why the
+pre-commit-hooks package is included in Debian.
+
+The above example can be replicated the following way:
+
+  --- .pre-commit-config.yaml ---
+  repos:
+  -   repo: local
+      hooks:
+      -   id: end-of-file-fixer
+          name: end-of-file-fixer
+          entry: end-of-file-fixer
+          language: system
+      -   id: trailing-whitespace-fixer
+          name: trailing-whitespace-fixer
+          entry: trailing-whitespace-fixer
+          language: system
+      -   id: name-tests-test
+          name: name-tests-test
+          entry: name-test-test
+          language: system
+  [...]
+  ---
+
+In future, the Debian package pre-commit-hooks might include some simplification
+(like an include file) way to reference these local pre-commit-hooks easier.
+
+ -- Daniel Baumann <daniel@debian.org>  Mon, 21 Apr 2025 12:55:47 +0200