Update README

[dANW34V3R]

This pull request addresses the issue raised in #1196 by adding a section to the README

[TommyMurphyTM1234]

I don't undertstand why the recommendation is as follows:

It is recommended to do clean builds to avoid problems with outdated stamp
files. This can be done with the following commands where $RISCV is the
install path used by the previous build:

   rm -r $RISCV
   git clean -fXd

rather than simply

make distclean

or maybe

make distclean
rm -rf <configure--prefix-dir>

[dANW34V3R]

I simply took the recommendation from stefanct. Happy for it to be either way round as long as it it documented somewhere visible

[TommyMurphyTM1234]

I simply took the recommendation from stefanct. Happy for it to be either way round as long as it it documented somewhere visible

Seems to me that something based on make distclean would be more appropriate than manually deleting stuff (other than the actual --prefix directory which presumably needs to be manually deleted?)? In any case, I don't see that your suggested approach deletes the stamps files which I thought was key? I think that the correct way(s?) to do a "clean" need clarification and maybe explanation as the situation doesn't seem clear to me.

[dANW34V3R]

I think that the correct way(s?) to do a "clean" need clarification and maybe explanation as the situation doesn't seem clear to me.

I agree, it is not clear to me either as per #1196 giving multiple, different suggestions. This should be resolved ASAP however as it can cause unclear build issues as seen in #1240, who is best to consult?