Generic/UselessOverridingMethod: improve documentation description and

titles

- <documentation> title now matches the sniff title.
- <standard> description uses 'discouraged' instead of 'should not' as
this sniff raises a warning and not an error.
- Minor grammar fixes and small changes to hopefully improve the
readability of the <standard> description and <code> titles.

Author: rodrigoprimo

src/Standards/Generic/Docs/CodeAnalysis/UselessOverridingMethodStandard.xml

@@ -1,11 +1,11 @@
-<documentation title="Useless Overriding Methods">
+<documentation title="Useless Overriding Method">
     <standard>
     <![CDATA[
-    Methods should not be defined that only call the parent method.
+    It is discouraged to override a method if the overriding method only calls the parent method.
     ]]>
     </standard>
     <code_comparison>
-        <code title="Valid: A method that extends functionality on a parent method.">
+        <code title="Valid: A method that extends functionality of a parent method.">
         <![CDATA[
 final class Foo extends Baz
 {
@@ -17,7 +17,7 @@ final class Foo extends Baz
 }
         ]]>
         </code>
-        <code title="Invalid: An overriding method that only calls the parent.">
+        <code title="Invalid: An overriding method that only calls the parent method.">
         <![CDATA[
 final class Foo extends Baz
 {