[0.7 QA] Profiling Tutorial page is broken

[digantdesai]

🐛 Multiple small issues under one GH Issue,

(1) examples/devtools/build_example_runner.sh referred from https://docs.pytorch.org/executorch/0.7/tutorials/devtools-integration-tutorial.html does not work.

It runs into several issues.

• EXECUTORCH_BUILD_EXTENSION_FLAT_TENSOR is not enabled
• CMake Error at kernels/optimized/CMakeLists.txt:61 (add_library): No SOURCES given to target: optimized_kernels`

(2) The Google Colab notebook doesn't work because we first need to install ExecuTorch on that machine?

(3) https://docs.pytorch.org/executorch/0.7/using-executorch-troubleshooting.html#next-steps 3rd bullet URL is incorrect

Versions

executorch==0.7.0a0+729f9a3

cc @Gasoonjia