Add the bin directory to your PATH before whatever directory contains your system's go binary. bin contains bin/go, a script which uses the appropriate Go installation for your architecture (see the go directory). You can now use the go command as normal.
The two packages which should be used by normal consumers are the xtrace/client and xtrace/grpcutil packages. Both have their primary documentation in doc comments in the code; view using the standard go doc tools or godoc.org.
xtrace/client provides an X-Trace client that provides a simple logging interface. xtrace/grpcutil provides utility functions for standard grpc functions that propagate X-Trace state.
The local package (which you shouldn't have to import directly, but is used by the xtrace/client package) requires code to be rewritten in order to work properly. Use the tool in cmd/rewrite to rewrite each package that you want to be capable of propagating X-Trace state when new goroutines are spawned. Note that some standard library or third party packages could spawn goroutines which call callbacks which, if defined in your code, could contain logging statements or gRPC calls that need to consume or propagate X-Trace state; you may want to rewrite these packages in addition to your own packages. Rewriting standard library packages has not been thoroughly tested, but it should in theory be completely safe.