message: Update documentation for custom rewrite specs.
diff: @@ -127,14 +127,16 @@ consists of defining a pattern as well as adding a C++ function to perform the
  replacement:
  ```td {.td}
  -def : Pat<(TF_LeakyReluOp $arg, F32Attr:$a),
  - (cOp<"createTFLLeakyRelu"> $arg, $a)>;
  +def createTFLLeakyRelu : NativeCodeCall<
  + "createTFLLeakyRelu($_builder, $0->getDefiningOp(), $1, $2)">;
  +
  +def : Pat<(TF_LeakyReluOp:$old_value, $arg, F32Attr:$a),
  + (createTFLLeakyRelu $old_value, $arg, $a)>;
  ```
  ```c++
  -static Value *createTFLLeakyRelu(Operation *op, ArrayRef<Value *> operands,
  - ArrayRef<Attribute> attrs,
  - PatternRewriter &rewriter) {
  +static Value* createTFLLeakyRelu(PatternRewriter &rewriter, Operation *op,
  + Value* operand, Attribute attr) {
  return rewriter.create<mlir::TFL::LeakyReluOp>(
  op->getLoc(), operands[0]->getType(), /*arg=*/operands[0],
  /*alpha=*/attrs[0].cast<FloatAttr>());
  