README incorrectly implies that age-plugin-yubikey broadly supports PIV tokens

[RespiteSage]

The age README file says that

Hardware PIV tokens such as YubiKeys are supported through the age-plugin-yubikey plugin.

but age-plugin-yubikey only supports a particular subset of PIV tokens (per this issue, P256 tokens in the 20 "retired" slots).

This isn't a huge issue, but clarifying the language might save someone else the time it took me to try out age-plugin-yubikey and look through issues before I found the issue linked above.

I think something like

Some PIV tokens, including YubiKeys, are supported through the age-plugin-yubikey plugin.

would be enough of a change.

[str4d]

I replied to the duplicate of this in my repo: str4d/rage#541 (comment)

tl;dr "PIV token" means the hardware device, not the key material stored on it.

[RespiteSage]

I'm continuing the discussion in the rage issue. If our discussion reaches a conclusion there, I'll add a summary here in a comment.