chore(readme): explain how to use a locally built runner

README.md

@@ -48,6 +48,13 @@ cd end-to-end
 
 ## Running from locally built binary
 
+Before injecting a manually built binary, make sure a simple test was
+run so that the directories are populated.
+
+### Forgejo
+
+From a checkout of https://codeberg.org/forgejo/forgejo/
+
 ```sh
 make TAGS='bindata sqlite sqlite_unlock_notify' generate forgejo
 cp -a forgejo /srv/forgejo-binaries/forgejo-10.0
@@ -55,6 +62,15 @@ cp -a forgejo /srv/forgejo-binaries/forgejo-10.0
 
 It will be used whenever the version `10.0` is specified in a test.
 
+### Forgejo runner
+
+From a checkout of https://code.forgejo.org/forgejo/runner
+
+```sh
+make --always-make forgejo-runner
+cp forgejo-runner /tmp/forgejo-end-to-end/forgejo-runner
+```
+
 ## Running actions locally
 
 To run and debug workflows from `actions/example-*`, from the root of