Add local pre-push validation gates

Co-authored-by: Andrew Kesterson <andrew@starfort.tech>

README.md

@@ -43,6 +43,26 @@ cmake --build build
 cmake --install build
 ```
 
+## Local pre-push checks
+
+Enable the repository's local pre-push checks once in each clone:
+
+```bash
+git config core.hooksPath .githooks
+```
+
+The hook runs cppcheck when `scripts/cppcheck.sh` and cppcheck are available,
+then the default build and tests, followed by the `AKERR_USE_STDLIB=OFF`
+build and tests. Builds are kept under `.git/akerr-prepush` and do not disturb
+the normal `build/` directory. Mutation testing is opt-in because it is slow:
+
+```bash
+AKERR_HOOK_MUTATION=1 git push
+```
+
+CI remains the hard gate. For an intentional local escape, use Git's standard
+`git push --no-verify` option.
+
 The library depends on `stdlib` and on POSIX threads. Both are optional at the
 cost of some functionality — see [docs/building.md](docs/building.md) for
 `-DAKERR_USE_STDLIB=OFF` and