Updates the install script to auto-detect custom installs
Updates the install script to auto-detect custom installs

grpc/homebrew-grpc,grpc/homebrew-grpc,vmlinz/homebrew-grpc,tbetbetbe/homebrew-grpc,stanley-cheung/homebrew-grpc,mwoytowich/homebrew-grpc,vmlinz/homebrew-grpc,w4-sjcho/homebrew-grpc,w4-sjcho/homebrew-grpc,jtattermusch/homebrew-grpc,mwoytowich/homebrew-grpc,stanley-cheung/homebrew-grpc,jtattermusch/homebrew-grpc,tbetbetbe/homebrew-grpc