Fix up the README, see #53

README.md

@@ -5,10 +5,14 @@ the docker images used to build the various clang compilers used on the site.
 
 ## To Test
 
-* `sudo docker build -t clangbuilder .`
-* `sudo docker run clangbuilder ./build.sh trunk`
+This assumes you have set up your user account to be able to run
+`docker` [without being root](https://docs.docker.com/engine/security/rootless/);
+if you haven't done so, you'll need to prefix these commands with `sudo`.
+
+* `docker build --build-arg image=22.04 -t clangbuilder .`
+* `docker run clangbuilder ./build.sh trunk`
 
 ### Alternative to run (for better debugging)
 
-* `sudo docker run -t -i clangbuilder bash`
+* `docker run -t -i clangbuilder bash`
 * `./build.sh trunk`