Allow adding documentation to secrets

[pbiggar]

When a user adds a secret, there's often useful information to go with it, such as a description, or how to set it or change it. As I add some API keys to an app, I find I want a link to the documentation, and also a link to how to change the key. If possible, a user might want to link to the upstream "resource" (maybe a page for that key on the vendor's dashboard).

[StachuDotNet]

merged this issue into #5260