Fixing js example and cleaning up one sentence (#2172)

Summary:
**Summary**

Cleaning up JS example to have proper order. Cleaning up sentence to be clearer.

**Test Plan**

NA
Pull Request resolved: #2172

Differential Revision: D17306067

Pulled By: Daniel15

fbshipit-source-id: 25d94313dde4157dbea192007ece110add9d5360

Author: lizlecrone

docs/Advanced-Topics-Entities.md

@@ -77,9 +77,9 @@ the `getEntityAt()` method on a `ContentBlock` object, passing in the target
 offset value.
 
 ```js
+const contentState = editorState.getCurrentContent();
 const blockWithLinkAtBeginning = contentState.getBlockForKey('...');
 const linkKey = blockWithLinkAtBeginning.getEntityAt(0);
-const contentState = editorState.getCurrentContent();
 const linkInstance = contentState.getEntity(linkKey);
 const {url} = linkInstance.getData();
 ```
@@ -100,8 +100,7 @@ from the text. Entities with this mutability type are effectively atomic.
 
 For instance, in a Facebook input, add a mention for a Page (e.g. Barack Obama).
 Then, either add a character within the mentioned text, or try to delete a character.
-Note that when adding characters, the entity is removed, and when deleting character,
-the entire entity is removed.
+Note that when adding or deleting characters, the entity is removed.
 
 This mutability value is useful in cases where the text absolutely must match
 its relevant metadata, and may not be altered.