specify which path we're matching

This wasn't clear to me, when I run `depcruise --validate .dependency-cruiser.json src`, exactly what I was trying to match in that regex. (relative to here? relative to src? relative to the file, as passed to `import` ?)

Thank you for making this tool and publishing and documenting it! This was really useful yesterday in identifying a circular dependency in TypeScript, which mocha totally barfs on.

doc/rules-reference.md

@@ -137,6 +137,8 @@ out dependency-cruiser will assume it to be `warn`.
 A regular expression an end of a dependency should match to be catched by this
 rule.
 
+In `from`, this is the path from project root to the file containing a dependency. In `to`, this is the path from project root to the file the dependency resolves to.
+
 When path is in a `to` part of a rule it accepts the regular expression
 'group matching' special variables `$0`, `$1`, `$2`, ...  as well. See
 'group matching' below for an explanation & example.