Document code size measurements

[yanesca]

Consult @tom-cosgrove-arm or @tom-daubney-arm and add a step-by-step description on how to do code size measurements to /kb/how-to/non-functional-testing.md (create the file if it doesn't exist yet).

[tom-daubney-arm]

Hi @yanesca, Do you want step by step instructions on how to do it with the script which is soon to be merged in #7426 or would you like instructions on how to do it without using the script? Happy to provide either.

[yanesca]

I was thinking of the soon to be merged script. We don't want to do anything fancy with it or anything different. The goal is to measure code size the same way as everyone else.

[tom-daubney-arm]

I agree, I am happy to add this.

[yanesca]

Thank you very much!