Created fib_go.go, the Go file that implements fib using recursion.
Created fib_go-th.go, the Go file that implements fib using recursion and go routines.
Added fib_go and fib_go-th targets to Makefile.
Added descriptions for fib_go and fib_go-th targets in README.
Updated general project description in README.
Minor: Had to fix formatting for other targets.