docs: clarify supported tls cipher suites

Signed-off-by: Alex Gavin <a_gavin@icloud.com>

docs/https.md

@@ -56,6 +56,9 @@ tls_server_config:
   # Go default cipher suites are used. Available cipher suites are documented
   # in the go documentation:
   # https://golang.org/pkg/crypto/tls/#pkg-constants
+  #
+  # Note that only the cipher returned by the following function are supported:
+  # https://pkg.go.dev/crypto/tls#CipherSuites
   [ cipher_suites:
     [ - <string> ] ]