rg --debug should output information about ignore files being read.

Currently it outputs something like the following, but it is not clear where the patterns are coming from:

% rg --no-config --debug foo
DEBUG|rg::args|src/args.rs:544: not reading config files because --no-config is present
DEBUG|grep_regex::literal|grep-regex/src/literal.rs:59: literal prefixes detected: Literals {

Is it possible to add an option -prune, to not explore sub-directories, when the current directory has been matched ? (like find -prune)