Added -r option to README.md

Author: federivo

README.md

@@ -70,6 +70,11 @@ upload content to https://gist.github.com/.
  gist -l : all gists for authed user
  gist -l defunkt : list defunkt's public gists
 
+To read a gist and print it to STDOUT
+
+ gist -r GIST_ID
+ gist -r 374130
+
 ‌See `gist --help` for more detail.
 
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