vty: Document some previously undocumented parameters

Katerina pointed out that some nodes are not fully documented and
proposed some messages. The token/timeout messages were correct, I
have modified the other messages. I removed the full-stop from the
PING/PONG documentation as we are normally not using a full sentence.
diff --git a/openbsc/src/libbsc/bsc_vty.c b/openbsc/src/libbsc/bsc_vty.c
index ec92c18..a59397f 100644
--- a/openbsc/src/libbsc/bsc_vty.c
+++ b/openbsc/src/libbsc/bsc_vty.c
@@ -2644,7 +2644,7 @@
 DEFUN(cfg_ts_pchan,
       cfg_ts_pchan_cmd,
       "phys_chan_config PCHAN", /* dynamically generated! */
-      "Physical Channel configuration (TCH/SDCCH/...)")
+      "Physical Channel configuration (TCH/SDCCH/...)\n" "Physical Channel\n")
 {
 	struct gsm_bts_trx_ts *ts = vty->index;
 	int pchanc;
@@ -2663,7 +2663,7 @@
 DEFUN_HIDDEN(cfg_ts_pchan_compat,
       cfg_ts_pchan_compat_cmd,
       "phys_chan_config PCHAN",
-      "Physical Channel configuration (TCH/SDCCH/...)")
+      "Physical Channel configuration (TCH/SDCCH/...)\n" "Physical Channel\n")
 {
 	struct gsm_bts_trx_ts *ts = vty->index;
 	int pchanc;