Add steps to README for adding a configuration package

README.org

@@ -1,3 +1,5 @@
+* Installing
+
   To use this repository execute the following commands in Emacs:
 
   #+begin_src emacs-lisp
@@ -5,3 +7,35 @@ To use this repository execute the following commands in Emacs:
     (package-refresh-contents)
     (package-install 'oni-package)
   #+end_src
+
+* Adding new configurations
+
+  When you add a new configuration file, also add at least a test that it
+  actually gets loaded:
+
+  : tests/integration/oni-example-mode.bats
+
+  #+begin_src bats
+    #!/usr/bin/env bats
+
+    @test "Opening a .example file loads oni-example-mode" {
+        run emacs -batch -l package -f package-initialize \
+            -visit test.example \
+            -eval "(prin1 (featurep 'oni-example-mode))"
+
+        echo "$output"
+
+        [[ "$output" == "t" ]]
+    }
+  #+end_src
+
+  And add the integration test in =.gitlab.yaml=:
+
+  #+begin_src yaml
+    integration-test-oni-example-mode:
+      stage: integration-test
+      image: registry.gitlab.com/ryuslash/emacs-config
+      dependencies:
+        - package
+      script: make integration-test-oni-example-mode TEST_ARCHIVE=$(realpath bin/)
+  #+end_src