Mention djhtml in contributing section of the README

Author: JelteF

README.md

@@ -79,12 +79,12 @@ admin interface, go back to the main interface. You're now logged in.
 
 ## Contributing
 
-Code formatting and linting is done using [`ruff`] and [`biome`]. You can run
-formatting using `make format`. Linting can be done using `make lint` and
-automatic fixing of linting errors can be done using `make lint-fix` or `make
-lint-fix-unsafe` (unsafe fixes can slightly change program behaviour, but often
-the fixed behaviour is the one you intended). You can also run both `make
-format` and `make lint-fix-unsafe` together by using `make fix`. CI
+Code formatting and linting is done using [`ruff`], [`biome`], and [`djhtml`].
+You can run formatting using `make format`. Linting can be done using `make
+lint` and automatic fixing of linting errors can be done using `make lint-fix`
+or `make lint-fix-unsafe` (unsafe fixes can slightly change program behaviour,
+but often the fixed behaviour is the one you intended). You can also run both
+`make format` and `make lint-fix-unsafe` together by using `make fix`. CI
 automatically checks that you adhere to these coding standards.
 
 You can install the git pre-commit hook to help you adhere to the codestyle:
@@ -95,6 +95,7 @@ ln -s ../../tools/githook/pre-commit .git/hooks/
 
 [`ruff`]: https://docs.astral.sh/ruff/
 [`biome`]: https://biomejs.dev/
+[`djhtml`]: https://github.com/rtts/djhtml
 
 ### Discord