Readme instructions for compile unclear

[maclobdell]

The readme specifies the following command for compile.

mbed compile -t GCC_ARM -m [target] --profile release --app-config=configs/.json

This doesn't work because you need to explicitly specify the configuration file to use.

It would be of great help to the user to include an intermediate step that asks them to choose the flash layout and other configuration choices.

[maclobdell]

also, from experimentation, the way to get the smallest code size is with GCC_ARM compiler and the tiny.json profile.

So, I recommend the documenation be updated to something like this:

mbed compile -t GCC_ARM -m [target] --profile tiny.json --app-config=configs/[your chosen config].json