diff --git a/README.md b/README.md
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--- /dev/null
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+# Raspberry PI Alpine Linux Image Builder
+
+Create minimal Linux images based on [Alpine Linux](https://alpinelinux.org/)
+for the [Raspberry PI](https://www.raspberrypi.org/).
+
+
+## Features
+
+* Alpine base
+  * Small image size
+  * Fast image build
+* A/B partition schema
+  * Simple update of whole system
+  * Fallback if update failed
+* Single image for every Raspberry PI
+* Read only root filesystem
+
+
+## Usage
+
+### Image Creation
+
+> A simple example for a go application can be found in the [example](example/) 
+> directory.
+
+To generate an empty image simply run:
+```
+docker run --rm -it -v $PWD/output:/output bboehmke/raspi-alpine-builder
+```
+
+This will create 2 image files in the directory `$PWD/output/`:
+* `alpine.img.gz`: complete SD card image for the raspberry
+* `alpine_update.img.gz`: image of root partition to update running raspberry
+
+> For each image a *.sha256 file will be generated to validate integrity.
+
+To add custom modifications mount a script to `/input/image.sh`.
+The following variables can be useful for the for and `image.sh`:
+
+| Variable    | Description                 |
+| ----------- | --------------------------- |
+| INPUT_PATH  | Path to input directory     |
+| ROOTFS_PATH | Path to new root filesystem |
+| BOOTFS_PATH | Path to new boot filesystem |
+| DATAFS_PATH | Path to new data filesystem |
+
+There is also a function `chroot_exec` that can be used to run command inside 
+the new root filesystem. To enable a service called `example_daemon` simple run:
+```
+chroot_exec rc-update add example_daemon default
+```
+
+#### Config Variables
+
+The following variables can be used to modify the base behaviour of the image 
+builder.
+
+| Variable              | Default Value                        | Description                      |
+| --------------------- | ------------------------------------ | -------------------------------- |
+| ALPINE_MIRROR         | http://dl-cdn.alpinelinux.org/alpine | Mirror used for package download |
+| ALPINE_BRANCH         | 3.10                                 | [Alpine Branch](https://wiki.alpinelinux.org/wiki/Alpine_Linux:Releases) to use for image |
+| DEFAULT_TIMEZONE      | Etc/UTC                              | Default [Timezone](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones) to use for image |
+| DEFAULT_HOSTNAME      | alpine                               | Default hostname |
+| DEFAULT_ROOT_PASSWORD | alpine                               | Default password for root user |
+| SIZE_BOOT             | 100M                                 | Size of boot partition |
+| SIZE_ROOT_FS          | 200M                                 | Size of root file system |
+| SIZE_ROOT_PART        | 500M                                 | Size of root partition |
+| SIZE_DATA             | 20M                                  | Initial Size of data partition |
+| IMG_NAME              | sdcard                               | Base name of created image file |
+
+### Update running system
+
+The system can be updated without a complete flash of the SD card from the 
+running system with the following steps:
+
+1. Transfer the update image to the running system
+2. (Optional) Validate integrity of image with checksum file
+3. Write the image to the actual inactive partition
+4. Switch active partition
+5. Reboot system
+
+> An example implementation can be found in the helper script 
+> [ab_flash](resources/scripts/ab_flash)
+
+## Image structure
+
+### Partition Layout
+
+The image contains 4 partitions:
+
+1. **Boot:** (Size: `SIZE_BOOT`) \
+   Contains boot loader and boot configuration
+    
+2. **Root A:** (Size: `SIZE_ROOT_PART`) \
+   Contains complete root filesystem including all required kernels
+
+3. **Root B:** (Size: `SIZE_ROOT_PART`) \
+   Same as *Root A*
+
+4. **Data:** (Size: Initial `SIZE_DATA` & increases on first start) \
+   Contains persistent data for both root partitions
+
+> With the exception of the data partition every partition is mounted read only
+
+The A/B root partitions enables an easy and reliable way to update the complete 
+system. This is done by flashing the inactive partition with a new root 
+filesystem and make this partition active. If this new filesystem does not boot
+the boot loader will fallback to the old partition.
+
+The root file system should be as small as possible to reduce the update time 
+later. To support future increase of the root file system the partition should 
+contain some free space.
+
+### Boot loader
+
+To support the A/B partition schema the [U-Boot](https://www.denx.de/wiki/U-Boot)
+boot loader is used.
+
+The configuration/script for the boot loader can be found in the 
+[boot.cmd](resources/boot.cmd). This will boot the active root partition and 
+switch the active partition if the active one will not start.
+> This script also select the right kernel for old Raspberry PIs
+
+The image contains a simple tool that resets the boot counter and switch the 
+active partition from the running OS. The sources of the script can be found 
+in the [uboot.c](resources/uboot.c). 
+
diff --git a/resources/build.sh b/resources/build.sh
index 10d8735..45b4a12 100755
--- a/resources/build.sh
+++ b/resources/build.sh
@@ -15,7 +15,7 @@ set -e
 : ${SIZE_ROOT_FS:="200M"}
 : ${SIZE_ROOT_PART:="500M"}
 : ${SIZE_DATA:="20M"}
-: ${IMG_NAME:="alpine-${ALPINE_BRANCH}-sdcard"}
+: ${IMG_NAME:="sdcard"}
 
 
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