Update html-end-tags doc (#228)

* Update html-end-tags doc

* Improve wording

docs/rules/html-end-tags.md

@@ -2,17 +2,12 @@
 
 - :wrench: The `--fix` option on the [command line](http://eslint.org/docs/user-guide/command-line-interface#fix) can automatically fix some of the problems reported by this rule.
 
-This rule enforce the way of end tags.
-
-- [Void elements] disallow end tags.
-- Other elements require end tags.
-
 ## :book: Rule Details
 
-This rule reports the following elements:
+This rule reports:
 
-- [Void elements] which have end tags.
-- Other elements which do not have end tags and are not self-closing.
+- presence of and end tag on [Void elements](https://www.w3.org/TR/html51/syntax.html#void-elements)
+- absence of both an end tag (e.g. `</div>`) and a self-closing opening tag (e.g. `<div/>`) on other elements
 
 :-1: Examples of **incorrect** code for this rule:
 
@@ -37,9 +32,3 @@ This rule reports the following elements:
 ## :wrench: Options
 
 Nothing.
-
-[Void elements]: https://www.w3.org/TR/html51/syntax.html#void-elements
-
-## TODO: `<br></br>`
-
-`parse5` does not recognize the illegal end tags of void elements.