Add contribution informations.

CONTRIBUTING.md

@@ -0,0 +1,35 @@
+<!-- markdownlint-disable MD001 MD013 -->
+
+# Contributing
+
+Below are the ways you can contribute to this package. Thank you for giving your time to improve it.
+
+## [Issues](https://github.com/llemaitre19/jtsx/issues)
+
+Report bugs, request changes or enhancements, ...
+
+## [Discussions](https://github.com/llemaitre19/jtsx/discussions)
+
+Share ideas or suggestions, discuss functional or technical choices, ...
+
+## [Pull Requests](https://github.com/llemaitre19/jtsx/pulls)
+
+Contribute with your own code to the repository. 
+
+### Writing code
+
+* Coding best practices: [Emacs Lisp style guide](https://github.com/bbatsov/emacs-lisp-style-guide).
+
+### Running tests locally (on your Emacs current version)
+
+* Install [Eask](https://emacs-eask.github.io/).
+* Run `make`.
+
+### Running tests locally across all supported versions of Emacs
+
+* Install the [Nix package manager](https://nixos.org/download/).
+* Run `make test_all`.
+
+### Checking Github test workflow
+
+* After pushing on your `jtsx` fork, go to `Actions` tab and check whether the test workflow has succeeded.

Makefile

@@ -37,7 +37,7 @@ lint:
 	$(EASK) lint package
 
 test_all:
-	@echo "Testing against all Emacs versions..."
+	@echo "Testing across all Emacs versions..."
 	(cd tests && ./run-tests.bash)
 
 cross_install:

README.md

@@ -221,3 +221,8 @@ An invalid `JSX` syntax in the buffer can be the source of the problem. `Tree-si
 ### Why another major mode for editing `JSX` ?
 
 Although popular [`web-mode`](https://github.com/fxbois/web-mode) and [`rjsx-mode`](https://github.com/felipeochoa/rjsx-mode) are very good packages for `JSX` edition, they have been written when Emacs built-in `JSX` support was very poor or absent. Currently, Emacs comes with a pretty good `JSX` / `TSX` support and even gives the possibility to use `Tree-sitter` integration. `jtsx` takes advantage of these new features to provide a lightweight package targetting both `JSX` and `TSX` with some handy functionalities.
+
+
+## Contributing
+
+All kinds of contributions are welcome: issues, discussions, or pull requests. More informations [here](./CONTRIBUTING.md).