update agent cli usage

cmd/drone-agent/main.go

@@ -45,7 +45,7 @@ func main() {
 		cli.BoolTFlag{
 			EnvVar: "DRONE_DEBUG",
 			Name:   "debug",
-			Usage:  "start the agent in debug mode",
+			Usage:  "enable agent debug mode",
 		},
 		cli.BoolFlag{
 			EnvVar: "DRONE_DEBUG_PRETTY",
@@ -60,36 +60,39 @@ func main() {
 		cli.StringFlag{
 			EnvVar: "DRONE_HOSTNAME,HOSTNAME",
 			Name:   "hostname",
+			Usage:  "agent hostname",
 		},
 		cli.StringFlag{
 			EnvVar: "DRONE_PLATFORM",
 			Name:   "platform",
+			Usage:  "restrict builds by platform conditions",
 			Value:  "linux/amd64",
 		},
 		cli.StringFlag{
 			EnvVar: "DRONE_FILTER",
 			Name:   "filter",
-			Usage:  "filter expression used to restrict builds by label",
+			Usage:  "filter expression to restrict builds by label",
 		},
 		cli.IntFlag{
 			EnvVar: "DRONE_MAX_PROCS",
 			Name:   "max-procs",
+			Usage:  "agent parallel builds",
 			Value:  1,
 		},
 		cli.BoolTFlag{
 			EnvVar: "DRONE_HEALTHCHECK",
 			Name:   "healthcheck",
-			Usage:  "enables the healthcheck endpoint",
+			Usage:  "enable healthcheck endpoint",
 		},
 		cli.DurationFlag{
 			EnvVar: "DRONE_KEEPALIVE_TIME",
 			Name:   "keepalive-time",
-			Usage:  "after a duration of this time if the agent doesn't see any activity it pings the server to see if the transport is still alive",
+			Usage:  "after a duration of this time of no activity, the agent pings the server to check if the transport is still alive",
 		},
 		cli.DurationFlag{
 			EnvVar: "DRONE_KEEPALIVE_TIMEOUT",
 			Name:   "keepalive-timeout",
-			Usage:  "after having pinged for keepalive check, the client waits for a duration of Timeout and if no activity is seen even after that the connection is closed.",
+			Usage:  "after pinging for a keepalive check, the agent waits for a duration of this time before closing the connection if no activity",
 			Value:  time.Second * 20,
 		},
 	}