Update README

Signed-off-by: Tomás Senart <tsenart@gmail.com>

README.md

@@ -86,6 +86,8 @@ attack command:
  Send body with chunked transfer encoding
  -connections int
  Max open idle connections per target host (default 10000)
+ -dns-ttl value
+ Cache DNS lookups for the given duration [-1 = disabled, 0 = forever] (default 0s)
  -duration duration
  Duration of the test [0 = forever]
  -format string
@@ -109,7 +111,7 @@ attack command:
  -max-body value
  Maximum number of bytes to capture from response bodies. [-1 = no limit] (default -1)
  -max-connections int
-  Max connections per target host
+  Max connections per target host
  -max-workers uint
  Maximum number of workers (default 18446744073709551615)
  -name string
@@ -200,6 +202,11 @@ Specifies whether to send request bodies with the chunked transfer encoding.
 
 Specifies the maximum number of idle open connections per target host.
 
+#### `-dns-ttl`
+
+Specifies the duration to cache DNS lookups for. A zero value caches forever.
+A negative value disables caching altogether.
+
 #### `-max-connections`
 
 Specifies the maximum number of connections per target host.