docs: add no-important rule docs

Author: yannbertrand

README.md

@@ -60,6 +60,7 @@ export default [
 | :--------------------------------------------------------------- | :------------------------------- | :-------------: |
 | [`no-duplicate-imports`](./docs/rules/no-duplicate-imports.md)   | Disallow duplicate @import rules |       yes       |
 | [`no-empty-blocks`](./docs/rules/no-empty-blocks.md)             | Disallow empty blocks            |       yes       |
+| [`no-important`](./docs/rules/no-important.md)                   | Disallow !important annotations  |       yes       |
 | [`no-invalid-at-rules`](./docs/rules/no-invalid-at-rules.md)     | Disallow invalid at-rules        |       yes       |
 | [`no-invalid-properties`](./docs/rules/no-invalid-properties.md) | Disallow invalid properties      |       yes       |
 

docs/rules/no-important.md

@@ -0,0 +1,21 @@
+# no-important
+
+Disallow `!important` annotations.
+
+## Background
+
+Needing !important indicates there may be a larger underlying issue.
+
+## Rule Details
+
+Examples of incorrect code:
+
+```css
+a {
+	color: red !important;
+}
+
+a .link {
+	font-size: padding: 10px 20px 30px 40px !important;
+}
+```