fix vignette setup

Author: sbgraves237

DESCRIPTION

@@ -8,7 +8,13 @@ Maintainer: Spencer Graves <spencer.graves@prodsyse.com>
 Description: Search contributed R packages, sort by package.
 License: GPL (>= 2)
 Depends: brew
-Suggests: RODBC, WriteXLS, testthat 
+Suggests: 
+    RODBC,
+    WriteXLS,
+    testthat,
+    knitr,
+    rmarkdown
 Language: en-us
 URL: https://github.com/sbgraves237/sos
 BugReports: https://github.com/sbgraves237/sos/issues
+VignetteBuilder: knitr