Ship the GPL text, and show it in the installer

The repository declared GPL-3.0-or-later and carried no copy of it;
the Arch package pointed at the system's shared text and nothing else
needed one. The installer does: a licence page needs a file to show,
and the moment before installation is where the terms can still change
a decision. The standard text, at the root where every convention
looks for it, converted to CRLF at packaging time because a Windows
edit control draws a bare LF as nothing.

docker/windows/package.sh

@@ -32,6 +32,9 @@ STAGE="${OUT}/stage"
 rm -rf "${STAGE}"
 mkdir -p "${STAGE}/models"
 cp "${EXE}" "${STAGE}/darkroom.exe"
+# CRLF for the licence page: it is shown in a Windows edit control, which
+# draws a bare LF as nothing and runs the whole GPL together.
+sed 's/$/\r/' "${REPO}/LICENSE" > "${STAGE}/LICENSE"
 
 # The models, with the guard every other packager carries: an LFS pointer is
 # ~130 bytes and looks exactly like a model to `cp`. Shipped, it fails inside