Fixing C++ installation instructions.
Fixing C++ installation instructions.

PiperOrigin-RevId: 197889804
GitOrigin-RevId: 9c3a38ad86da03f0180fc87082bf7107c6d537fd

google/tink,google/tink,google/tink,google/tink,google/tink,google/tink,google/tink,google/tink