Add oidc-issuer-url arg to README

README.md

@@ -222,6 +222,7 @@ Usage of oauth2_proxy:
   -proxy-prefix string: the url root path that this proxy should be nested under (e.g. /<oauth2>/sign_in) (default "/oauth2")
   -redeem-url string: Token redemption endpoint
   -redirect-url string: the OAuth Redirect URL. ie: "https://internalapp.yourcompany.com/oauth2/callback"
+  -oidc-issuer-url: the OpenID Connect issuer URL. ie: "https://accounts.google.com"
   -request-logging: Log requests to stdout (default true)
   -request-logging-format: Template for request log lines (see "Logging Format" paragraph below)
   -resource string: The resource that is protected (Azure AD only)