docs: update the "Using the Immutable Data" guide

packages/dx-react-grid/docs/guides/immutability.md

@@ -1,8 +1,6 @@
 # Using the Immutable Data
 
-## Overview
-
-DevExpress Data Grid for React conforms to the React [optimization principles](https://facebook.github.io/react/docs/optimizing-performance.html). According to these principles, the Grid does n't mutate data passed through a state and uses memoization and [React.PureComponents](https://facebook.github.io/react/docs/react-api.html#react.purecomponent). A [React.PureComponent](https://facebook.github.io/react/docs/react-api.html#react.purecomponent) compares old and new state values using a simple comparison. In this case, if you update a state object field, React does not update the component because it compares two references to the same object. Immutable data structures [help](https://facebook.github.io/react/docs/optimizing-performance.html#the-power-of-not-mutating-data) to solve this problem.
+DevExpress Data Grid for React conforms to the React [optimization principles](https://facebook.github.io/react/docs/optimizing-performance.html). According to these principles, the Grid does not mutate data passed through a state and uses memoization and [React.PureComponents](https://facebook.github.io/react/docs/react-api.html#react.purecomponent). A `React.PureComponent` compares old and new state values using a simple comparison. In this case, if you update a state object field, React does not update the component because it compares two references to the same object. Immutable data structures [help](https://facebook.github.io/react/docs/optimizing-performance.html#the-power-of-not-mutating-data) to solve this problem.
 
 You can use the [seamless-immutable](https://github.com/rtfeldman/seamless-immutable) library to make a React Grid state immutable.
 The following example demonstrates how to initialize an immutable state: