please document SALSA_CI_BLHC_ARGS

I wanted to run blhc with this additional parameter: --ignore-line 'Compiling .*\.c[cu] .* > .*\.o' and found SALSA_CI_BLHC_ARGS in the pipeline source code, but no instructions how to properly use that, i.e. is it even possible to have a pattern which contains spaces? (And how would that have to be quoted?)

In my tests (https://salsa.debian.org/nvidia-team/nvidia-nccl) I only got to

$ blhc --debian --line-numbers --color ${SALSA_CI_BLHC_ARGS} ${WORKING_DIR}/*.build || [ $? -eq 1 ]
No such file: .*\.c[cu] at /usr/bin/blhc line 787.
checking '.*\.c[cu]'...