README: Update requirements and document cleaning up

Author: dos1

README.md

@@ -20,8 +20,22 @@ To launch the build, run:
 
 Use `./build.sh --sudo` if your user does not have permission to use Docker daemon, or `./build.sh --podman` if you want to use rootless Podman instead (untested).
 
-Directory `anbox-work` will be created where all AOSP sources will be downloaded to and where the build will be performed. You need about 150GB of free disk space and 16GB of RAM.
+Directory `anbox-work` will be created where all AOSP sources will be downloaded to and where the build will be performed. You'll need at least 60GB of free disk space and 16GB of RAM.
 
 ## Installation:
 
 Put the `anbox-work/vendor/anbox/android.img` file into `/var/lib/anbox/android.img` on your phone and reboot.
+
+## Cleanup
+
+By default incremental build will be performed. To start over from scratch:
+
+```
+rm -rf anbox-work
+```
+
+To start over without having to download sources again:
+
+```
+rm -rf anbox-work/* anbox-work/.patches anbox-work/.pc
+```