docs: document what postcss plugins do

packages/mc-scripts/postcss.config.js

@@ -17,25 +17,54 @@ module.exports = {
   parser: false,
   map: false,
   plugins: [
+    /**
+     * Plugin to transform `@import` rules by inlining content.
+     * https://github.com/postcss/postcss-import
+     */
     require('postcss-import')(),
+    /**
+     * Plugin to parse CSS and add vendor prefixes to CSS rules
+     * using values from "[Can I Use](https://caniuse.com/)".
+     * https://github.com/postcss/autoprefixer
+     */
     require('autoprefixer')({
+      // Enables `-ms-` prefixes for Grid Layout including some
+      // limited autoplacement support.
+      // https://github.com/postcss/autoprefixer#grid-autoplacement-support-in-ie
       grid: 'autoplace',
       overrideBrowserslist: browserslist.development,
     }),
+    /**
+     * Plugin to enable Custom Media Queries in CSS, following
+     * the [CSS Media Queries](https://drafts.csswg.org/mediaqueries-5/#custom-mq) specification.
+     * https://github.com/postcss/postcss-custom-media
+     */
     require('postcss-custom-media')({
       importFrom: safeResolvePath(
         '@commercetools-frontend/application-components',
         'materials/media-queries.css'
       ),
     }),
+    /**
+     * Plugin to enable Custom Properties in CSS, following
+     * the [CSS Custom Properties](https://www.w3.org/TR/css-variables-1/) specification.
+     * https://github.com/postcss/postcss-custom-properties
+     */
     require('postcss-custom-properties')({
       preserve: false,
       importFrom: safeResolvePath(
         '@commercetools-uikit/design-system',
         'materials/custom-properties.css'
       ),
     }),
+    // TODO: we should deprecate/remove this, as it's not maintained and it doesn't
+    // officially support postcss v8 yet.
     require('postcss-color-mod-function')(),
+    /**
+     * Plugin to `console.log()` the messages (warnings, etc.)
+     * registered by other PostCSS plugins.
+     * https://github.com/postcss/postcss-reporter
+     */
     require('postcss-reporter')(),
   ],
 };