docs(linter): improve the documentation of eslint/no-useless-concat (oxc-project#9179)

Relates to [oxc-project#6050](oxc-project#6050)

Adds correctness and incorrectness examples following rule documentation
template.

Author: therewillbecode

crates/oxc_linter/src/rules/eslint/no_useless_concat.rs

@@ -25,12 +25,31 @@ declare_oxc_lint!(
     ///
     /// ### Why is this bad?
     ///
-    /// It’s unnecessary to concatenate two strings together.
+    /// It’s unnecessary to concatenate two strings together when they could
+    /// be combined into a single literal.
     ///
-    /// ### Example
+    /// ### Examples
+    ///
+    /// Examples of **incorrect** code for this rule:
     /// ```javascript
     /// var foo = "a" + "b";
     /// ```
+    ///
+    /// ```javascript
+    /// var foo = 'a' + 'b' + 'c';
+    /// ```
+    ///
+    /// Examples of **correct** code for this rule:
+    /// ```javascript
+    /// var foo = 'a' + bar;
+    /// ```
+    ///
+    /// // when the string concatenation is multiline
+    /// ```javascript
+    /// var foo = 'a'
+    ///     + 'b'
+    ///     + 'c';
+    /// ```
     NoUselessConcat,
     eslint,
     suspicious