docs: add trufflehog entry

Author: joscha

README.md

@@ -383,6 +383,7 @@ clang-format supports.
 - [topiary](https://github.com/tweag/topiary)
 - [treefmt](https://github.com/numtide/treefmt)
 - [trim-trailing-whitespace](https://github.com/pre-commit/pre-commit-hooks/blob/main/pre_commit_hooks/trailing_whitespace_fixer.py)
+- [trufflehog](https://github.com/trufflesecurity/trufflehog): Secret scanner
 
 ### Custom hooks