chore: update CONTRIBUTING guide

CONTRIBUTING.md

@@ -1,7 +1,6 @@
 # Contributing
 
-Hi! We're glad you'd like to contribute to the project. Your help is essential
-in making this project substantial.
+Hi! We're glad you'd like to contribute to the project. Your help is essential in making this project substantial.
 
 If you are looking to make substantial changes, please [open an issue](https://github.com/abeidahmed/rails-heroicon/issues/new)
 first to discuss with us.
@@ -21,9 +20,12 @@ By participating in this project, you agree to abide by its rules.
 
 ## Adding new heroicons
 
-- Add solid icon(s) in `./icons/solid/` directory and outline icon(s) in
-  `./icons/outline/` directory
-- After adding the icon(s), run `./bin/compress`
-  (you may need to run `sudo chmod 755 ./bin/compress`)
+- Copy all icons from the [`optimized`](https://github.com/tailwindlabs/heroicons/tree/master/optimized) directory in this order:
+    - [`16/solid`](https://github.com/tailwindlabs/heroicons/tree/master/optimized/16/solid) -> `icons/micro`
+    - [`20/solid`](https://github.com/tailwindlabs/heroicons/tree/master/optimized/20/solid) -> `icons/mini`
+    - [`24/solid`](https://github.com/tailwindlabs/heroicons/tree/master/optimized/24/solid) -> `icons/solid`
+    - [`24/outline`](https://github.com/tailwindlabs/heroicons/tree/master/optimized/24/solid) -> `icons/outline`
+- After adding the icon(s), run `./bin/compress` (you may need to run `sudo chmod 755 ./bin/compress`)
+- Update the `CHANGELOG.md`
 - Submit a pull request adhering to the above mentioned guidelines
 - That's it. You have made a significant contribution