explain my conflicted attitude to code contributions

doc/index.md

@@ -98,3 +98,23 @@ To see how commands are implemented, read the code in `command.fnl`.
 There is a simple keymap in `dunlin.fnl`, and you can see the details
 of how keymaps work in `keymap.fnl`
 
+
+## Contributing
+
+If you like (or see the potential in) Dunlin enough to want to
+contribute to it, that is awesome and you have just made my day!
+
+However, I need to point out that it's under active development:
+my vision for how it'll end up is indefinite in some places and
+poorly articulated in others. So, please, don't send me code
+that you're personally invested in and would be disappointed if
+I reject/ignore it because it doesn't fit some plan that you
+didn't know about when you wrote it.
+
+You can checkout Dunlin from https://gti.telent.net/dan/dunlin. I
+haven't put it on Github because I have uneasy feelings about the
+ongoing centralisation of Open Source, but certainly don't let that
+stop you. You can [email me your change](mailto:dan@telent.net) as a
+patch, or you can point me at code on your preferred source code
+hosting service - whatever works for you. I reserve the right to be
+less flexible in future if I start drowning in changes.