Fix typo in SA1600 documentation

Author: bsivanov

documentation/SA1600.md

@@ -29,7 +29,7 @@ A violation of this rule occurs if an element is completely missing a documentat
 
 To fix a violation of this rule, add or fill-in a documentation header for the element.
 
-the following example shows a method with a valid documentation header:
+The following example shows a method with a valid documentation header:
 
 ```csharp
 /// <summary>