Fix a couple of issues in README.md under the Windows section [skip ci] (#2217)
Fix a couple of issues in README.md under the Windows section [skip ci] (#2217)

The chocolately command was not copy/paste friendly. This fixes that. Note that
the leading space is intentional since we are doing a line continuation. Also,
the other parts of the guide mention installing git, so we add that as well to
be consistent.
googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp