feat: improve error handling, some docs, stubs

README.md

@@ -1,2 +1,10 @@
 # oidclogin
 OpenID Connect Login SDK written in Go for Gin.
+
+The following environment variables are expected to be set:
+```env
+OIDC_CLIENT_ID=<client id>
+OIDC_CLIENT_SECRET=<client secret>
+OIDC_ISSUE=<issuer url>
+```
+If these env vars are not present, then depending on configuration, stubs will be used for the endpoints or the program will crash