Improve contirbuting instructions
Improve contirbuting instructions

Signed-off-by: Yuri Shkuro <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@ysh.us>

jaegertracing/jaeger,jaegertracing/jaeger,jaegertracing/jaeger,jaegertracing/jaeger,jaegertracing/jaeger