Add documentation link in Cargo.toml

[DJDuque]

Whenever you search for openssh in crates.io, this will add a "Documentation" link under the crate's name. This removes the annoying extra click of going into the crate's README if you know you only want to get to the documentation.

[jonhoo]

This change is 

[NobodyXu]

Wait, why is it closed?
Did I accidentally close it?

[jonhoo]

Ah, so, this is actually a shortcoming of crates.io: rust-lang/crates.io#1484. I'm hesitant to add a documentation link like that because it'll always point to the latest documentation, which will be wrong if someone is looking at an older version of openssh on crates.io.

[DJDuque]

That is a fair point, although I believe that the latest documentation is still a reasonable entry point; it reduces the number of clicks needed for everybody. People looking for older versions still need to go README -> Versions -> Select older version -> Documentation link of that older version; here they could just go Latest documentation -> from the top left, choose whatever version.

But leaving out the documentation link is also reasonable.

[jonhoo]

Fair enough, I buy that. Let's merge it!

[jonhoo]

Released as 0.9.4 🎉