Document new builder location on ghcr.io

The commands currently documented download an old version of the builder
which lead to errors during build since the images on Docker Hub still
used cas:
```
Error: rpc error: code = Unavailable desc = connection error: desc = "transport: Error while dialing dial tcp 3.33.152.147:443: i/o timeout"
```

README.md

@@ -165,19 +165,19 @@ Options:
 amd64:
 
 ```bash
-docker pull homeassistant/amd64-builder
+docker pull ghcr.io/home-assistant/amd64-builder:latest
 ```
 
-armv7/armhf:
+armv7:
 
 ```bash
-docker pull homeassistant/armv7-builder
+docker pull ghcr.io/home-assistant/armv7-builder:latest
 ```
 
 aarch64:
 
 ```bash
-docker pull homeassistant/aarch64-builder
+docker pull ghcr.io/home-assistant/aarch64-builder:latest
 ```
 
 ## Run
@@ -189,7 +189,7 @@ docker run \
 	--rm \
 	--privileged \
 	-v ~/.docker:/root/.docker \
-	homeassistant/amd64-builder \
+    ghcr.io/home-assistant/amd64-builder:latest \
 		--all \
 		-t addon-folder \
 		-r https://github.com/xy/addons \
@@ -204,7 +204,7 @@ docker run \
 	--privileged \
 	-v ~/.docker:/root/.docker \
 	-v /my_addon:/data \
-	homeassistant/amd64-builder \
+    ghcr.io/home-assistant/amd64-builder:latest \
 		--all \
 		-t /data
 ```
@@ -220,13 +220,36 @@ docker run \
 	-v ~/.docker:/root/.docker \
 	-v /var/run/docker.sock:/var/run/docker.sock:ro \
 	-v /my_addon:/data \
-	homeassistant/amd64-builder \
+    ghcr.io/home-assistant/amd64-builder:latest \
 		--all \
 		-t /data
 ```
 
+### Using shell alias
+
+On Linux, it can be helpful to use a shell alias to run the builder from the
+current directory. E.g. by adding the following function to your `~/.bashrc`:
+
+```
+function builder() {
+	docker run \
+	  --rm \
+	  -it \
+	  --privileged \
+	  -v ${PWD}:/data \
+	  -v /var/run/docker.sock:/var/run/docker.sock:ro \
+      ghcr.io/home-assistant/amd64-builder:latest --target /data $@
+}
+```
+
+This allows to build add-ons e.g. for a single architecture as follow:
+```
+$ cd /path/to/your/add-on
+$ builder --amd64 --docker-hub agners
+```
+
 ## Help
 
 ```bash
-docker run --rm --privileged homeassistant/amd64-builder --help
+docker run --rm --privileged ghcr.io/home-assistant/amd64-builder:latest --help
 ```