[RFA 1/3] Add usage to printf command

[Tom Tromey <tom@tromey.com>]

This patch adds the "Usage:" text to the printf command's help text,
and tries to improve the text a tiny bit.

gdb/ChangeLog
2018-02-14  Tom Tromey  <tom@tromey.com>

	* printcmd.c (_initialize_printcmd): Add usage to printf.
---
 gdb/ChangeLog  | 4 ++++
 gdb/printcmd.c | 5 +++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/gdb/printcmd.c b/gdb/printcmd.c
index fc9d7e4dd9..13b967f0a2 100644
--- a/gdb/printcmd.c
+++ b/gdb/printcmd.c
@@ -2680,8 +2680,9 @@ No argument means cancel all automatic-display expressions.\n\
 Do \"info display\" to see current list of code numbers."), &deletelist);
 
   add_com ("printf", class_vars, printf_command, _("\
-printf \"printf format string\", arg1, arg2, arg3, ..., argn\n\
-This is useful for formatted output in user-defined commands."));
+Formatted printing, like the C \"printf\" function.\n\
+Usage: printf \"format string\", arg1, arg2, arg3, ..., argn\n\
+This supports most C printf format specifications, like %s, %d, etc."));
 
   add_com ("output", class_vars, output_command, _("\
 Like \"print\" but don't put in value history and don't print newline.\n\
-- 
2.13.6