Correct spelling of "of"

:)

Author: jonbulica99

doc/10-How-it-works.md

@@ -1,7 +1,7 @@
 <a id="How-it-works"></a>How it works
 =====================================
 
-This chapter wants to give you some basic understanding off how the
+This chapter wants to give you some basic understanding of how the
 Director works with your Icinga installation. At least once you start
 to work with satellite zones it might be worth to give this a read.