Add a section of Wallet invocation

[paulbastian]

OpenID4VP has a (small) section on how the Wallet shall be launched/invoked/started.
At least copying the section would not seem like a bad idea to me.

Especially section at https://openid.github.io/OpenID4VCI/openid-4-verifiable-credential-issuance-wg-draft.html#section-4.1-1

The Credential Issuer sends Credential Offer using an HTTP GET request or an HTTP redirect to the Wallet's Credential Offer Endpoint defined in Section 11.1.

does not match what many wallets have implemented today. Rather referencing to a Wallet Invocation Section may be a better solution.

[peppelinux]

I agree, Wallet Invocation is something very particular in this field and it worth of a dedicated section (security considerations included I would add)

[Sakurann]

I agree. redirect and GET are definitely not the only options. I tried clarify this in PR #246. please review and comment if it meets your expectations.

[jogu]

Some or maybe all of this is probably resolved by the fix for #13, PR #380