docs: align subject case rule in readme #3159 (#3179)

Update the scope-case rule in docs/reference-rules and config-conventional/README to be same.

Author: lxow456

@commitlint/config-conventional/README.md

@@ -92,7 +92,7 @@ echo "fix(scope): some message" # passes
 #### subject-case
 
 - **condition**: `subject` is in one of the cases `['sentence-case', 'start-case', 'pascal-case', 'upper-case']`
-- **rule**: `never`
+- **rule**: `always`
 - **level**: `error`
 
 ```sh

docs/reference-rules.md

@@ -278,12 +278,12 @@ Infinity
 
 #### subject-case
 
-- **condition**: `subject` is in case `value`
+- **condition**: `subject` is in one of the cases `['sentence-case', 'start-case', 'pascal-case', 'upper-case']`
 - **rule**: `always`
 - **value**
 
 ```
-'lower-case'
+['sentence-case', 'start-case', 'pascal-case', 'upper-case']
 ```
 
 - **possible values**