docs: add name and description to example SAML2 backend

[melanger]

These attributes are required to generate valid metadata in combination with required_attributes and/or optional_attributes.

Without these attributes specified (and there is no hint in pysaml2 docs about this either), the generated metadata contains empty <ns0:ServiceName xml:lang="en" /> inside AttributeConsumingService, which is invalid. This was probably the cause of pysaml2#345

[melanger]

Please consider updating the docs as well and/or adding a check for this in code, either here or in pysaml2.

[c00kiemon5ter]

thank you!