fix incrby (#141)

Author: amitanandaiyer

content/latest/yedis/api/incrby.md

@@ -14,9 +14,9 @@ showAsideToc: true
 ---
 
 ## Synopsis
-<b>`INCR key`</b><br>
-This command adds 1 to the number that is associated with the given `key`. The numeric value must a 64-bit signed integer.
-<li>If the `key` does not exist, the associated string is set to "0".</li>
+<b>`INCRBY key delta`</b><br>
+This command adds `delta` to the number that is associated with the given `key`. The numeric value must a 64-bit signed integer.
+<li>If the `key` does not exist, the associated string is set to "0" before performing the operation.</li>
 <li>If the given `key` is associated with a non-string value, or if its associated string cannot be converted to an integer, an error is raised.</li>
 
 ## Return Value