README: Add notes about Zephyr 3.7 LTS

This commit adds notes about retrieving the correct version of Docker
image for the Zephyr 3.7 LTS.

Signed-off-by: Stephanos Ioannidis <[email protected]>

README.md

@@ -27,20 +27,40 @@ building most Zephyr targets.
 The pre-built developer docker image is available on both GitHub Container Registry (`ghcr.io`) and
 DockerHub (`docker.io`).
 
-**GitHub Container Registry (`ghcr.io`)**
+For Zephyr 3.7 LTS, use the `v0.26-branch` or the latest `v0.26.x` release Docker image.
+
+##### GitHub Container Registry (`ghcr.io`)
+
+###### Current Zephyr versions
 
 ```
 docker run -ti -v $HOME/Work/zephyrproject:/workdir \
            ghcr.io/zephyrproject-rtos/zephyr-build:main
 ```
 
-**DockerHub (`docker.io`)**
+###### Zephyr 3.7 LTS
+
+```
+docker run -ti -v $HOME/Work/zephyrproject:/workdir \
+           ghcr.io/zephyrproject-rtos/zephyr-build:v0.26-branch
+```
+
+##### DockerHub (`docker.io`)
+
+###### Current Zephyr versions
 
 ```
 docker run -ti -v $HOME/Work/zephyrproject:/workdir \
            docker.io/zephyrprojectrtos/zephyr-build:main
 ```
 
+###### Zephyr 3.7 LTS
+
+```
+docker run -ti -v $HOME/Work/zephyrproject:/workdir \
+           docker.io/zephyrprojectrtos/zephyr-build:v0.26-branch
+```
+
 #### Building Developer Docker Image
 
 The developer docker image can be built using the following command: