update readme

Signed-off-by: gbionescu <[email protected]>

README.md

@@ -1,14 +1,21 @@
 # Rootfs image builder
 
-This repo builds an `ext4` or an `initrd` using Docker containers.
+This repo builds root filesystem images or initrd images based on Docker containers.
 
 Note: *some assembly required.*
 
-## Prerequisites
+Images are generated by:
+1. Pulling a base image from Docker Hub.
+2. Installing systemd or any other init system. Alpine uses OpenRC while Amazon Linux and Ubuntu use systemd.
+3. Installs sshd and other utilities to make the image usable.
+4. Sets `root:root` as the default user and password.
+5. Packs the docker container into a rootfs/initrd image.
+
+See the [releases](https://github.com/gbionescu/build-rootfs/releases) page for pre-built images and kernel.
 
-Your user needs to be able to run `docker`.
+## Prerequisites
 
-If not, run scripts with sudo: `sudo build-rootfs.sh`.
+Have `docker` installed.
 
 ## Building a rootfs
 
@@ -20,10 +27,10 @@ Simply run:
 
 Where `rootfs-type` is one of the root filesystem generators that starts with `type-`.
 
-For example, to generate an `Ubuntu 21.04` rootfs, run:
+For example, to generate an `alpine` rootfs, run:
 
 ```bash
-./build-rootfs.sh ubuntu21.04
+./build-rootfs.sh alpine
 ```
 
 Notes:
@@ -68,7 +75,19 @@ twice because systemd needs to be initialized.
 
 Just add a new folder with the 3 files described above
 
+### Tests
+
+Currently the built-in tests build the rootfs for all the types and run them with QEMU.
+
+Tests poll the serial console output for the `login:` prompt.
+
+To run the tests, simply run:
+
+```bash
+./tests/test-all.sh
+```
+
 ## Troubleshooting
 
 - Need a larger image? Change `init-rootfs.sh`.
-
+- Need to install more packages? Change `inside-container.sh`.