tests: add missing boilerplate

testcases/t/198-regression-scratchpad-crash.t

@@ -1,5 +1,19 @@
 #!perl
 # vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
 # When using a command which moves a window to scratchpad from an invisible
 # (e.g. unfocused) workspace and immediately shows that window again, i3
 # crashed.