Didgeridoo magizine had a few things here and there on didge music theory. Its based on drum rythems.

I've said many times that "the type of didjeridu I like to play" will play 5 main notes. The fundamental drone, two jaw drops down, and two toots up.. Of course it's possible to play 3 or 4 or more toots up on some didjs with some styles of armeture.

So, you could theoretically write out something in bass clef,, but to me it's more of a percussive instrument, so you'd probably be more concerned with remembering and notating the percussive aspects..

I've spent about seven years now working on Afro-Cuban drumming, and every time I learn something new it's written down. We have our own script where a note below the staff means right hand, and above means left. Then, there's a hollow note meaning open tone, closed note means bass, X means slap, a strike through means a muffled tone, and a T means a touch.. We have really only two timing sequences. 6/8 and 4/4.
But, the writing is more of a way to share with other players, more than it is a compositional tool or creative outlet.
I could see how you could write out didj stuff.. Shouldn't be that hard!
Dave