add instructions for Setting up Mill in CI and mention FORCE_COLOR

Author: lihaoyi

website/docs/modules/ROOT/images/basic/ForceColor0.png

@@ -389,6 +389,37 @@ going on. It contains regular Mill output accompanied by additional BSP
 client-server communication details. This can be useful to look at if your
 IDE fails to import your Mill project
 
+
+== Setting up Mill in CI
+
+Due to Mill's usage of xref:#_bootstrap_scripts[Bootstrap Scripts], you typically do not
+need to setup anything in your CI system to make Mill work. Any Mill project should be
+buildable via `./mill` on your CI machines without needing to first install Java, Mill,
+or other dependencies, and the `./mill` bootstrap script will download these dependencies
+as necessary.
+
+One thing that you should set up manually is to enable a https://force-color.org/[FORCE_COLOR]
+environment variable in your CI system. For example, in Github Actions this can be configured
+in your workflow `.yml` file via:
+
+```yaml
+env:
+  FORCE_COLOR: '1'
+```
+
+`FORCE_COLOR` ensures Mill produces ANSI-colored output logs despite being called
+programmatically in on your CI machines. Most CI systems process and render ANSI
+colors nicely in the browser, and this can make your CI logs much easier to read
+than if they were black-and-white:
+
+**Without FORCE_COLOR**
+
+image::basic/ForceColor0.png[]
+
+**With FORCE_COLOR=1**
+
+image::basic/ForceColor1.png[]
+
 == Using Mill without access to Maven Central
 
 Under some circumstances (e.g. corporate firewalls), you may not have access maven central.