Mention CMAKE_BUILD_TYPE on build instructions.
Mention CMAKE_BUILD_TYPE on build instructions.

And recommend RelWithDebInfo.  See also issue #145.

apitrace/apitrace,tuanthng/apitrace,tuanthng/apitrace,apitrace/apitrace,trtt/apitrace,swq0553/apitrace,joshua5201/apitrace,trtt/apitrace,joshua5201/apitrace,schulmar/apitrace,tuanthng/apitrace,trtt/apitrace,EoD/apitrace,tuanthng/apitrace,schulmar/apitrace,EoD/apitrace,apitrace/apitrace,joshua5201/apitrace,swq0553/apitrace,tuanthng/apitrace,EoD/apitrace,surround-io/apitrace,surround-io/apitrace,schulmar/apitrace,EoD/apitrace,trtt/apitrace,schulmar/apitrace,surround-io/apitrace,apitrace/apitrace,swq0553/apitrace,joshua5201/apitrace,swq0553/apitrace,joshua5201/apitrace,EoD/apitrace,schulmar/apitrace,surround-io/apitrace,swq0553/apitrace,trtt/apitrace,surround-io/apitrace