Add README section for end-to-end tests

README.md

@@ -43,6 +43,35 @@ application on the open internet; I just hacked it together for
 testing on localhost during development and it's probably hilariously
 insecure.
 
+## End-to-End Tests
+
+There's a (fairly minimal at the moment) end-to-end test suite defined
+in [tests.scm](./tests.scm).  To run it you'll need:
+
+- [Guile](https://www.gnu.org/software/guile/) again (no substitute
+  this time, sorry)
+- [guile-json](https://github.com/aconchillo/guile-json)
+- Firefox
+
+I'm also pretty sure it won't work on a non-POSIX system, though I
+haven't tried it.
+
+Given that's all sorted, you should be able to run:
+
+```
+guile tests.scm
+```
+
+It will print a JUint XML report to standard out, you can pretty-print
+it with:
+
+```
+guile tests.scm | xmllint --format -
+```
+
+Though, of course, this will require that you have `xmllint` on your
+system.
+
 ## Peripherals
 
 ### Terminal