all: add format strings

README.md

@@ -14,13 +14,15 @@ If you still want to, `make install` will install this utility to
 ## Usage
 
 ```
-Usage: bin/n [options]
+Usage: n [options]
 Options:
-  -h HOST, --host=HOST  NTP server to use
+  -h HOST, --host=HOST        NTP server to use
              defaults to 'europe.pool.ntp.org'
-  -p PORT, --port=PORT  NTP server port to use (must be numerical)
+  -p PORT, --port=PORT        NTP server port to use (must be numerical)
              defaults to '123'
-  --help                Display this message and exit
+  -f FORMAT, --format=FORMAT  Date format string (passed to strftime)
+             defaults to standard of ctime
+  --help                      Display this message and exit
 ```
 
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