build: Include various interesting files in tarballs

README.md and the demos are documentation that could be useful to
install, the spec file can be used by rpmbuild -ta, and the autogen.sh
and editor and uncrustify configuration could be useful for distro
packagers contributing patches upstream from a tree based on tarball
imports.

I arbitrarily left out CI configuration for PAPR and Travis-CI, since
these always take their source code from git anyway.

git.mk is excluded because it contains comments saying it should be.

Signed-off-by: Simon McVittie <smcv@collabora.com>

Closes: #236
Approved by: giuseppe

Makefile.am

@@ -1,6 +1,18 @@
 AM_CFLAGS = $(WARN_CFLAGS)
 CLEANFILES =
-EXTRA_DIST =
+EXTRA_DIST = \
+	.dir-locals.el \
+	.editorconfig \
+	README.md \
+	autogen.sh \
+	demos/bubblewrap-shell.sh \
+	demos/flatpak-run.sh \
+	demos/flatpak.bpf \
+	demos/userns-block-fd.py \
+	packaging/bubblewrap.spec \
+	uncrustify.cfg \
+	uncrustify.sh \
+	$(NULL)
 
 GITIGNOREFILES = build-aux/ gtk-doc.make config.h.in aclocal.m4