Documentation fix --with-sulgin

[pwFoo]

Here is an typo: https://github.com/troglobit/finit/blob/master/doc/build.md#example

--with-sulgin: Enable bundled sulogin program. Default is to use the system sulogin(8). The sulogin shipped with Finit allows password-less login if the root user is disabled or has no password at all.

Missing "o" in --with-sulgin.