Document `psk_list` parameter of ssl_server2 example program
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index b6e8a1d..ec23c8a 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -201,8 +201,12 @@
#endif /* MBEDTLS_X509_CRT_PARSE_C */
#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
-#define USAGE_PSK \
- " psk=%%s default: \"\" (in hex, without 0x)\n" \
+#define USAGE_PSK \
+ " psk=%%s default: \"\" (in hex, without 0x)\n" \
+ " psk_list=%%s default: \"\"\n" \
+ " A list of (PSK identity, PSK value) pairs.\n" \
+ " The PSK values are in hex, without 0x.\n" \
+ " id1,psk1[,id2,psk2[,...]]\n" \
" psk_identity=%%s default: \"Client_identity\"\n"
#else
#define USAGE_PSK ""