Document include/exclude filters properly

[Mark-Simulacrum]

We currently support include=... and exclude=... on the rust-timer build/queue invocations; documented here: https://perf.rust-lang.org/help.html.

However, that documentation wasn't updated when we adjusted those in #1279.

We should (a) update the documentation and (b) consider adding support for the other CLI flags to be parsed. I personally think it's probably not worth the effort to support more flags; in practice these are rarely used and collecting a full suite isn't that much slower (given CI times etc) than a partial one. That could change with runtime benchmarks being added though.

[lqd]

The first task to update the help page will be done by #1434