Notifying about index completion

[rmrnc]

Hi,
expanding on our PR #221, we are currently exploring a simple gRPC-based notification scheme for stenotype's index creation (more on that in a later post). To prevent rejection of a subsequent PR later on, we'd like to enquire whether moving from stenotype's current GNU-Makefile to a CMake-build configuration handling protoc's code generation would be acceptable to you.

[gconnell]

I'd be supportive of this, go for it 👍