README.md: expand credit for original

[IanDarwin]

Sudo was invented on Berkeley Unix on a VAX, and the current version is maintained by Todd Miller of the OpenBSD Unix project. It is thus correct to refer to the original as Unix/Linux as it is not a project originated by the Linux developers.

[omnivagant]

Better, but I would call the sudo project just "the sudo project", with a reference to the sudo project and with less occurances of "Unix/Linux" in the README because it gets pretty repetitive.

[IanDarwin]

@omnivagant Point taken, 2nd commit revises accordingly. Thanks.