Update documentation to reference 'config.toml' instead of 'config'. #7323
Description
Describe the problem you are trying to solve
After #7273, we now support loading 'config.toml' and 'credentials.toml' in place of the same files without extension, which used to be the default. Files with extensions are easier for people to edit due to syntax highlighting, etc.
Describe the solution you'd like
We should update all Cargo documentation to mention 'config.toml' and 'credentials.toml' so people use those by default instead of the versions without extension.