docs: user-guide rules updates (#650)

* Update descriptions in space-tab-mixed-disabled.md

Update grammar and readability.
Add Example

* add attr-lowercase example

* Update alt-require doc

docs/user-guide/rules/alt-require.md

@@ -4,10 +4,10 @@ title: alt-require
 keywords:
   - alt
   - image
-  - accessiblity
+  - accessibility
 ---
 
-Alt of img must be present and alt of area[href] and input[type=image] must be set value.
+Alt of `img` must be present and alt of area[href] and input[type=image] must be set with a value.
 
 Level: warning
 
@@ -16,7 +16,7 @@ Level: warning
 1. true: enable rule
 2. false: disable rule
 
-The following pattern are **not** considered violations:
+The following pattern are **not** considered rule violations:
 
 <!-- prettier-ignore -->
 ```html
@@ -25,7 +25,7 @@ The following pattern are **not** considered violations:
 <area shape="circle" coords="180,139,14" href="test.html" alt="test" />
 ```
 
-The following pattern is considered violation:
+The following pattern is considered a rule violation:
 
 <!-- prettier-ignore -->
 ```html

docs/user-guide/rules/attr-lowercase.md

@@ -13,14 +13,24 @@ Level: `error`
 2. false: disable rule
 3. ['viewBox', 'Test']: enable rule except for the given attribute names
 
-The following pattern is **not** considered a violation:
+### Example
+
+```json
+{
+  ...
+  "attr-lowercase": ['viewBox']
+  ...
+}
+```
+
+The following pattern is **not** considered a rule violation:
 
 <!-- prettier-ignore -->
 ```html
 <img src="test.png" alt="test" />
 ```
 
-The following pattern is considered a violation:
+The following pattern is considered a rule violation:
 
 <!-- prettier-ignore -->
 ```html

docs/user-guide/rules/space-tab-mixed-disabled.md

@@ -1,28 +1,38 @@
 ---
 id: space-tab-mixed-disabled
-title: space-tab-mixed-disabled
+title: space-tab-mixed-disabled # consider renaming to blankspace
 ---
 
-Spaces and tabs can not mixed in front of line.
+Blank-space (space and tab) characters should not be mixed in the beginning of any line.
 
 Level: `warning`
 
-## Config value
+## Config values
 
-1. space: space mode (only space for indentation)
-2. space4: space mode and require length
-3. tab: tab mode (only tab for indentation)
+1. space: space mode (only spaces are valid for indentation)
+2. space4: space mode and require 4 space characters
+3. tab: tab mode (only tab characters are valid for indentation)
 4. false: disable rule
 
-The following pattern are **not** considered violations:
+### Example
+
+```json
+{
+  ...
+  "space-tab-mixed-disabled": space4
+  ...
+}
+```
+
+The following patterns are **not** considered rule violations:
 
 <!-- prettier-ignore -->
 ```html
    →   →<img src="tab.png" />
 ········<img src="space.png" />
 ```
 
-The following pattern is considered violation:
+The following pattern is considered a rule violation:
 
 <!-- prettier-ignore -->
 ```html