Update command usage info

README.md

@@ -25,11 +25,11 @@ To solve this problem, `mego` accepts as arguments a path of file(s) containing
 ```
 Usage of mego:
 
-mego [-l SPEED] [-s] MEGA_LINK... LIST_PATH...
+mego [-l SPEED] [-r DURATION] [-s] MEGA_LINK... LIST_PATH...
 
-  -l uint     speed limit passed to megadl as --limit-speed
-  -s          silent mode. do not pipe megadl's stdout nor stderr
-  -r          interval between two retries
+  -l uint       speed limit passed to megadl as --limit-speed
+  -r duration   interval between two retries (default 1m0s)
+  -s            silent mode. do not pipe megadl's stdout nor stderr
 ```
 
 NB: The whole content of a *list file* is read and kept in memory. Every time a file is downloaded, the content of the *list file* will be overwritten. So please do not use a *list file* as a queue during execution.