Documentation - Feature to run an option platform specific script on the first boot

[olivier-singla]

I added the ability to run an optional platform specific script on the first boot. This will be useful in the case of doing some switch specific setup and initialization.

See the code change here:
#2531

This is the change in the documentation in order to document this feature.
https://gist.github.com/olivier-singla/992492e59d55631a2f78648656daacbb

[olivier-singla]

I was able to perform the platform initialization using the platform debian package. Therefore, the new feature I was proposing is no longer needed.