update docs

Author: mysticatea

Diff for: docs/rules/no-invalid-template-root.md

@@ -6,14 +6,19 @@ This rule checks whether every template root is valid.
 
 This rule reports the template root if the following cases:
 
+- The root is nothing. E.g. `<template></template>`.
 - The root is text. E.g. `<template>hello</template>`.
 - The root is multiple elements. E.g. `<template><div>one</div><div>two</div></template>`.
 - The root element has `v-for` directives. E.g. `<template><div v-for="x in list">{{x}}</div></template>`.
-- The root element has `v-if`/`v-else-if` directives without `v-else` elements. E.g. `<template><div v-if="foo">hello</div></template>`.
 - The root element is `<template>` or `<slot>` elements. E.g. `<template><template>hello</template></template>`.
 
 👎 Examples of **incorrect** code for this rule:
 
+```html
+<template>
+</template>
+```
+
 ```html
 <template>
     <div>hello</div>
@@ -33,17 +38,17 @@ This rule reports the template root if the following cases:
 </template>
 ```
 
+👍 Examples of **correct** code for this rule:
+
 ```html
 <template>
-    <div v-if="foo"></div>
+    <div>abc</div>
 </template>
 ```
 
-👍 Examples of **correct** code for this rule:
-
 ```html
 <template>
-    <div>abc</div>
+    <div v-if="foo"></div>
 </template>
 ```