Document the fact that option bundling is supported

[chocolateboy]

Short option bundling is supported e.g. -abc is equivalent to -a -b -c if they're boolean options or -a -bc if -b takes a parameter, but this isn't mentioned directly in the documentation.

This is the standard term e.g.:

Short options may be bundled, e.g. -a -b can be specified as -ab

[ORESoftware]

like with

git commit -am "foo"

I think the last letter in the group can take a parameter, so m can take a param in the above.
haven't verified that works with dashdash, but probably the standard way to it like git does.