add YYYY/.filelist files

A _YYYY/.filelist_ is a simple list of files for a given IOCCC year
that need to be present when building a _YYYY_ level compressed
tarball.  The list is relative to _docroot_ (top level repo directory).

We do not need a complex JSON file for such a simple list of files.
We only care about checking for the existence of files when forming
_YYYY_ level compressed tarball.

2001/.filelist

@@ -0,0 +1,10 @@
+2001/2001.tar.bz2
+2001/Makefile
+2001/README.md
+2001/.filelist
+2001/.gitignore
+2001/guidelines.txt
+2001/mkentry.c
+2001/rules.txt
+2001/.year
+var.mk