Update README

README.md

@@ -44,7 +44,34 @@ container first:
     $ make docker
 
 Note that building the image typically requires over an hour and 20 GB
-of disk space.
+of disk space, and it is only growing.
+
+The above command generates the development image as a subroutine. You
+can skip this and use the last tagged development image:
+
+    $ make docker-nobuild
+
+Or you can explicitly build the image without running it:
+
+    $ make image-dev
+
+The production image is based on the development one, with some
+additional layers. You can build it as follows:
+
+    $ make image-prod
+
+Lastly I should mention the tests. There are integration tests for
+every language, and they can be run as follows:
+
+    $ [CONCURRENCY=2] [TIMEOUT=5] yarn test [<filter>...]
+
+Filters can be for language (`python`, `java`) or test type (`hello`,
+`lsp`). You can comma-delimit multiple filters to do a disjunction,
+and space-delimit them to do a conjunction (`hello python,java`) for
+the `hello` tests for `python` and `java`.
+
+The tests are run automatically when building the production image,
+and fail the build if they fail.
 
 See also [riju-cdn](https://github.com/raxod502/riju-cdn).