📝 Add FAQ about custom domains

README.adoc

@@ -108,3 +108,15 @@ from the GitHub repository and (ii) `html` file when openning this page from the
 
 
 endif::[]
+
+== FAQ
+
+=== How can I configure a custom domain?
+
+GitHub Pages need a `CNAME` file on the `gh-pages` branch. But on every action run, the `gh-pages` branch is wiped out. To make a custom domain work, the easiest solution is to configure a pre build command:
+
+```yml
+pre_build: echo "your.custom.domain" > CNAME && git add -f CNAME
+```
+
+When you add this command to your action configuration, it will create the required `CNAME` file and add it to git.