[mlir] add initial chapters of the transform dialect tutorial

The transform dialect has been around for a while and is sufficiently
stable at this point. Add the first three chapters of the tutorial
describing its usage and extension.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D151491
diff --git a/mlir/examples/CMakeLists.txt b/mlir/examples/CMakeLists.txt
index 37c89d0..bdbba3e 100644
--- a/mlir/examples/CMakeLists.txt
+++ b/mlir/examples/CMakeLists.txt
@@ -1 +1,2 @@
 add_subdirectory(toy)
+add_subdirectory(transform)