Update migration guide

Author: hudochenkov

README.md

@@ -41,75 +41,18 @@ a {
 }
 ```
 
-## Migration from `1.x`
+## Migration from `2.x`
 
-If you have been using [predefined configs], you can look at [migrated predefined configs].
+Remove all `*-empty-line-before` and `clean-empty-lines` options. Use [stylelint] with `--fix` option instead.
 
-`sort-order` was split into [`order`](./docs/order.md) and [`properties-order`](./docs/properties-order.md).
-
-`properties-order` now uses an array of objects for grouping.
-
-`sort-order` keywords to new config conversion:
-
-| `1.x` | `2.x` |
-| --- | --- |
-| `@atrule` | `{ order: ["at-rules"] }`  or `{ order: [{ type: "at-rule" }] }` |
-| `@atrulename` | `{ order: [{ type: "at-rule", name: "atrulename" }] }` |
-| `@atrulename parameter` | `{ order: [{ type: "at-rule", name: "atrulename", parameter: "parameter" }] }` |
-| `>child` | `{ order: ["rules"] }` |
-| `$variable` | `{ order: ["custom-properties", "dollar-variables"] }` |
-| “leftovers” token `...` | `{ "unspecified-properties-position": "bottom" }` |
-
-Config for `1.x`:
-
-```js
-{
-	"sort-order": [
-		[
-			"$variable"
-		],
-		[
-			"margin",
-			"padding"
-		],
-		[
-			"border",
-			"background"
-		],
-		[
-			'...',
-			"at-rule",
-			"@include",
-			"@include media",
-			">child"
-		]
-	]
-}
-```
+`properties-order` doesn't support property groups. Convert it to simple array. Use [stylelint-order] with `--fix` option for empty line before property groups.
 
 Config for `2.x`:
 
-```js
+```json
 {
-	"order": [
-		"custom-properties",
-		"dollar-variables",
-		"declarations",
-		"at-rules",
-		{
-			"type": "at-rule",
-			"name": "include"
-		},
-		{
-			"type": "at-rule",
-			"name": "include",
-			"parameter": "icon"
-		},
-		"rules"
-	],
 	"properties-order": [
 		{
-			"emptyLineBefore": true,
 			"properties": [
 				"margin",
 				"padding"
@@ -122,8 +65,20 @@ Config for `2.x`:
 				"background"
 			]
 		}
-	],
-	"unspecified-properties-position": "bottom"
+	]
+}
+```
+
+Config for `3.x`:
+
+```json
+{
+	"properties-order": [
+		"margin",
+		"padding"
+		"border",
+		"background"
+	]
 }
 ```
 
@@ -205,8 +160,6 @@ If you want format style sheets, use [perfectionist] or [stylefmt], also a PostC
 [Sublime Text plugin]: https://github.com/hudochenkov/sublime-postcss-sorting
 [Atom plugin]: https://github.com/lysyi3m/atom-postcss-sorting
 [VS Code plugin]: https://github.com/mrmlnc/vscode-postcss-sorting
-[predefined configs]: https://github.com/hudochenkov/postcss-sorting/tree/ee71c3b61eea8fa11bc3aa2d26dd99a832df6d54/configs
-[migrated predefined configs]: https://gist.github.com/hudochenkov/b7127590d3013a5982ed90ad63a85306
 
 [Gulp PostCSS]: https://github.com/postcss/gulp-postcss
 [Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss