Compile docs out-of-date

[eoswald]

The docs say to compile gRPC using make however according to gRPC's repo, this is deprecated. From the compile docs:

After running make and sudo make install on the main directory, cd third_party/protobuf and do another sudo make install.

https://github.com/mymindstorm/matrix-appservice-mumble/blob/0.2.0-install-instructions/COMPILING_MURMUR.md

From the gRPC docs:

Building with make on UNIX systems (deprecated)
NOTE: make used to be gRPC's default build system, but we're no longer recommending it. You should use bazel or cmake instead. The Makefile is only intended for internal usage and is not meant for public consumption.

https://github.com/grpc/grpc/blob/master/BUILDING.md#building-with-make-on-unix-systems-deprecated

I am not sure if bazel or cmake will automatically compile protoc in third_party/. When I ran bazel it didn't seem like it but I could be mistaken.

Edit: Output when trying to sudo make install:

~/grpc-make$ sudo make install

Installing via 'make' is no longer supported. Use cmake or bazel instead.

Please consult BUILDING.md to get more information.

make: *** [Makefile:707: stop] Error 1

[mymindstorm]

Yes, looking at the blame, I wrote those docs before the deprecation. I will have to recompile murmur and see what needs to be changed.