[doc] Grid auto flow

[BravinJoshua]

The documentation is incomplete

[philipp-spiess]

Hey there! I know the answer is a bit late and maybe we've added it to the old docs in the meantime but just wanna let you know that we have this in our new documentation now: https://tailwindcss.com/docs/grid-auto-flow

Let us know if you still see any incompleteteness 👍