Supported toolchains declaration

[Carldkennedy]

Do we want to explicitly say we will support those toolchains, if yes, how? The latest 2 years worth etc...

I'm not averse to saying their available but at some point we want to explicitly declare our intentions in terms of EB toolchain support formally.

This page seems like the sensible place?

Originally posted by @jkwmoore in https://github.com/rcgsheffield/sheffield_hpc/pull/1794#discussion_r1192138541