Replace hardcoded credentials path with cargo docs link

[federicomenaquintero]

https://crates.io/settings/tokens incorrectly says ~/.cargo/credentials, it's missing the .toml in the filename.

[Turbo87]

for context: #5730

[LawnGnome]

OK, so if I'm reading the history correctly:

• Cargo added support for credentials.toml (with the extension) in 1.39.0 (November 2019).
• Cargo has created credentials.toml (with the extension) by default since 1.68.0 (March this year).

I guess my question is which of credentials and credentials.toml wins — if a user has a pre-existing credentials, and we tell them to add things to credentials.toml, is that going to break things?

Feels like it might be a little soon to make this change, but I'm interested in if anyone on the @rust-lang/cargo team has an opinion here?

[weihanglo]

I guess my question is which of credentials and credentials.toml wins — if a user has a pre-existing credentials, and we tell them to add things to credentials.toml, is that going to break things?

Nothing gonna be broken. credentials.toml would be ignored in that case.

Maybe just say it being saved in a local credential file and link to where The Cargo Book mentions it?

BTW just created rust-lang/cargo#12479 to clarify the situation. Thanks for the summary @LawnGnome :)

[Turbo87]

Maybe just say it being saved in a local credential file and link to where The Cargo Book mentions it?

that seems like a good idea to me. @federicomenaquintero could you amend the pull request accordingly? :)