kernel-shark: Modify FreeSans warning msg for GUI

Make the warning point out that the FreeSans font is required for the
kernelshark GUI. This is to alert the user that the GUI will not be made
when cmake does not detect FreeSans.

Signed-off-by: Solomon Tan <wjsota@gmail.com>
Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4ed8e89..c183f78 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,7 +69,7 @@
 
 else (TT_FONT_FILE)
 
-  message(WARNING "\nCould not find font ${KS_FONT}!\n")
+  message(WARNING "\nCould not find font ${KS_FONT}! Kernelshark GUI requires font ${KS_FONT}!\n")
 
 endif (TT_FONT_FILE)