Provide more examples

[JesusMcCloud]

We need more examples of typical tasks and self-contained ones at best. Redundancy with the regular docs is no reason not to list something under examples, because this is where stuff is really easy to find.

Missing:

• Creating a self-signed certificate

To be extracted from documentation

• Key generation
• Signing
• Verifying
• Parsing a certificate
• Evaluating a certificate extension
• creating a certificate extension with a custom ASN.1 Structure
• Creating a CSR
• Creating a self-signed certificate
• Verifying a COSE Signed
• Verifying a Signed JWT

@nodh @iaik-jheher @tlenz any more suggestions?