update README

Author: mrjbq7

README.md

@@ -31,4 +31,5 @@ const ta = @import("ta_lib");
 const prices = [_]f64{ 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 };
 
 const result = try ta.MOM(allocator, &prices, 5);
+defer allocator.free(result);
 ```