Clarify that it returns a hex string

sindresorhus · web-flow · commit 16e9f2802388 · 2019-03-21T23:45:30.000+07:00
#2
diff --git a/readme.md b/readme.md
@@ -26,6 +26,8 @@ cryptoRandomString(10);
 
 ### cryptoRandomString(length)
 
+Returns a [`hex`](https://en.wikipedia.org/wiki/Hexadecimal) string.
+
 #### length
 
 Type: `number`
