Document usage in Dart SASS

Closes #5.

README.md

@@ -1,20 +1,23 @@
 # hsl.scss
 
-[HSL colors](https://developer.mozilla.org/en-US/docs/Web/CSS/color_value#HSL_colors) [are awesome](https://www.sarasoueidan.com/blog/hex-rgb-to-hsl/). Unfortunately, the [SASS `hsl()` and `hsla()` functions](https://sass-lang.com/documentation/functions/color#hsl) converts the colors to RGB/RGBA format.
+[HSL colors](https://developer.mozilla.org/en-US/docs/Web/CSS/color_value#HSL_colors) [are awesome](https://www.sarasoueidan.com/blog/hex-rgb-to-hsl/). Unfortunately, under `node-sass` the [SASS `hsl()` and `hsla()` functions](https://sass-lang.com/documentation/functions/color#hsl) converts to other formats (hex or RGB/RGBA). And the situation [isn’t better in Dart SASS](https://github.com/meduzen/true-hsl.scss/issues/2).
 
-_hsl.scss_ replaces the two SASS functions by two others, preserving HSL(A) color declarations.
+_hsl.scss_ overwrites SASS `hsl` and `hsla` with passthrough functions, preserving HSL(A) color declarations without transformation nor validation.
 
 - [Demo](https://codepen.io/meduzen/pen/BaBKdBb?editors=0100#0)
 - [Tweet](https://twitter.com/meduzen/status/1161948600219459584) with screenshots.
 
 ## Installation
 
-1. `npm install hsl.scss` pulls the package into your project.
-2. `@import '~hsl.scss';` in a SCSS files make `hsl()` and `hsla()` available.
+`npm install hsl.scss -D` pulls the package into your project.
+
+- In a `node-sass` project, `@import 'hsl.scss';` in a SCSS files make `hsl()` and `hsla()` available.
+- In a Dart SASS project, `@use 'hsl.scss' as *` is required in every SCSS files where `hsl()` or `hsla()` are used.
 
 ## Usage
 
-Write regular CSS, the syntax is exactly the same:
+You can now expect `hsl` and `hsla` to behave like they do using standard CSS:
+
 ```scss
 :root {
 
@@ -39,12 +42,8 @@ Write regular CSS, the syntax is exactly the same:
 }
 ```
 
-## Before / after hsl.scss
+## Before / after `hsl.scss` when using `node-sass`
 
 ![Before: lot of issues. Now: no issues anymore.](https://pbs.twimg.com/media/ECASFaIWkAAHdni?format=jpg&name=large)
 
 ![Before: boring interpolation. Now: standard CSS.](https://pbs.twimg.com/media/ECASFaQXoAAjNqe?format=jpg&name=large)
-
-## Note
-
-There’s currently no test enforcing the validity of what is passed to `hsl()` and `hsla()`, like in CSS. They are _passthrough_ function.