Add troubleshooting information for Go and icu4c

What does this Merge Request do?

Add troubleshooting information for fixing:

# gitlab.com/gitlab-org/gitlab-elasticsearch-indexer
/usr/local/Cellar/go/1.14.2_1/libexec/pkg/tool/darwin_amd64/link: running clang failed: exit status 1
ld: warning: directory not found for option '-L/usr/local/Cellar/icu4c/64.2/lib'
ld: library not found for -licui18n
clang: error: linker command failed with exit code 1 (use -v to see invocation)

make[1]: *** [build] Error 2
make: *** [gitlab-elasticsearch-indexer/bin/gitlab-elasticsearch-indexer] Error 2

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.