Specify "union" merge strategy for the TODO file

This gives the semantics that I described in the previous
commit. Conflicts will be resolved by keeping both sides in the file,
and without conflict markers. This is not expected to be perfect, but
is expected to be easy for people to fix up without having to think
much about it.

diff --git a/.gitattributes b/.gitattributes
new file mode 100644 (file)
index 0000000..72c2395
--- /dev/null
+++ b/.gitattributes
@@ -0,0 +1 @@
+TODO merge=union