Add react/state-in-constructor to the list of rule in readme

Author: lukyth

README.md

@@ -133,6 +133,7 @@ Enable the rules that you would like to use.
 * [react/self-closing-comp](docs/rules/self-closing-comp.md): Prevent extra closing tags for components without children (fixable)
 * [react/sort-comp](docs/rules/sort-comp.md): Enforce component methods order (fixable)
 * [react/sort-prop-types](docs/rules/sort-prop-types.md): Enforce propTypes declarations alphabetical sorting
+* [react/state-in-constructor](docs/rules/state-in-constructor.md): Enforce the state initialization style to be either in a constructor or with a class property
 * [react/style-prop-object](docs/rules/style-prop-object.md): Enforce style prop value being an object
 * [react/void-dom-elements-no-children](docs/rules/void-dom-elements-no-children.md): Prevent void DOM elements (e.g. `<img />`, `<br />`) from receiving children