Fix QA issues of the devtools README (#5963)

Summary:
Pull Request resolved: #5963

Add new files in the "Directory structure".
And also remove an old statement. Since `-DEXECUTORCH_BUILD_DEVTOOLS=ON` is set in the build_example_runner.sh, and not in a command in the readme, so it no longer makes sense to call it out in this readme.

Reviewed By: Gasoonjia

Differential Revision: D64017662

fbshipit-source-id: 1ee8b086180c7f995ff3306ebceb4afcff934214

Author: Olivia-liu

examples/devtools/README.md

@@ -6,6 +6,9 @@ This directory contains examples of BundledProgram and ETDump generation.
 examples/devtools
 ├── scripts                           # Python scripts to illustrate export workflow of bundled program.
 ├── executor_runner                   # Contains an example for both BundledProgram to verify ExecuTorch model, and generate ETDump for runtime results.
+├── CMakeLists.txt                    # Example CMakeLists.txt for building executor_runner with Developer Tools support.
+├── build_example_runner.sh           # A convenient shell script to build the example_runner.
+├── test_example_runner.sh            # A convenient shell script to run the example_runner.
 └── README.md                         # Current file
 ```
 
@@ -46,7 +49,7 @@ python3 -m examples.devtools.scripts.export_bundled_program -m mv2 # for MobileN
 After exporting a `BundledProgram`, runtime profiling and debug data can be collected in an ``ETDump``. An ``ETDump`` is a buffer containing data generated by hooks within the ExecuTorch runtime.
 We offer an example runner that accepts a `BundledProgram` (`.bpte`) and runs a single iteration over the first method defined.
 
-Running the program will generate an `ETDump` file (`.etdp`) at the location specified by `--etdump_path`. Make sure to build the program as specified below to enable the event tracer.
+Running the program will generate an `ETDump` file (`.etdp`) at the location specified by `--etdump_path`.
 
 ```bash
    ./cmake-out/examples/devtools/example_runner --bundled_program_path mv2_bundled.bpte --etdump_path mv2_etdump.etdp