[mlir][emitc][NFC] Add an example to the description of the emitc.verbatim operation (#128004)

The official page provides an explanation of the **new** functionality
of `emitc.verbatim`, but a classic example in the `.td` file for this
operation is still missing.

Author: EtoAndruwa

mlir/include/mlir/Dialect/EmitC/IR/EmitC.td

@@ -1289,6 +1289,18 @@ def EmitC_VerbatimOp : EmitC_Op<"verbatim"> {
     `%dest` became `b` in the C code.
     `{{` in the format string is interpreted as a single `{` and doesn't introduce
     a placeholder.
+
+    Example:
+
+    ```mlir
+    emitc.verbatim "typedef float f32;"
+    emitc.verbatim "#pragma my var={} property" args %arg : f32
+    ```
+    ```c++
+    // Code emitted for the operation above.
+    typedef float f32;
+    #pragma my var=v1 property
+    ```
   }];
 
   let extraClassDeclaration = [{