add note on usage of OIDC_SET_COOKIE_APPEND in the sample config/doc
# state cookie: Lax
# session cookie: first time set Lax, updates (e.g. after inactivity timeout) Strict
# x_csrf discovery: Strict:
+#
+# The default `SameSite=None` cookie appendix on `Set-Cookie` response headers can be
+# conditionally overridden using an environment variable in the Apache config as in:
+# SetEnvIf User-Agent ".*IOS.*" OIDC_SET_COOKIE_APPEND=;
+# (since version 2.4.1)
+#
# When not defined the default is Off.
#OIDCCookieSameSite [On|Off]
