An instructional gap in generate-keys: Option 1

[superphiz]

https://medalla.launchpad.ethereum.org/generate-keys

Option 1: Use binary executable file

This step directs a user to download a zip/tarball file from a github release page but does not instruct the user to extract the binary from the zip. Failure to extract the binary causes the next step to fail. Option 1 should include instructions for extracting the zip/tarball. This issue appears consistent across the directions for all three platforms.

[unixpi]

@superphiz, while i haven't included specific instructions, I've tried to address that here.