Ignore cscope and main file

Different main.c files are stored in directory mains/ and can be copied to the main folder
diff --git a/sam3s_example/.gitignore b/sam3s_example/.gitignore
index f27dc92..d597181 100644
--- a/sam3s_example/.gitignore
+++ b/sam3s_example/.gitignore
@@ -3,3 +3,5 @@
 *~
 obj/
 build/
+cscope.out
+main.c