Match code examples in Solid OIDC and Solid OIDC Primer

[csarven]

Consider matching code examples, e.g., currently /oidc uses https://oidc.example and /oidc-primer uses https://secureauth.example . Alternatively, make obvious extensions, e.g., currently, /oidc uses https://app.example/id and /oidc-primer uses https://decentphtos.example/webid#this . /oidc-primer could instead use https://decentphotos.app.example/id , or change the example WebID in /oidc