Updated dockerhub readme to latest nifi version
This closes
## Latest changes
-### 1.8.0
+### 1.12.0
- The NiFi Toolkit has been added to the image under the path `/opt/nifi/nifi-toolkit-current` also set as the environment variable `NIFI_TOOLKIT_HOME`
- The installation directory and related environment variables are changed to be version-agnostic to `/opt/nifi/nifi-current`:
```
-docker run --rm --entrypoint /bin/bash apache/nifi:1.8.0 -c 'env | grep NIFI'
+docker run --rm --entrypoint /bin/bash apache/nifi:1.12.0 -c 'env | grep NIFI'
NIFI_HOME=/opt/nifi/nifi-current
NIFI_LOG_DIR=/opt/nifi/nifi-current/logs
NIFI_TOOLKIT_HOME=/opt/nifi/nifi-toolkit-current
@@ -28,7 +28,7 @@ NIFI_BASE_DIR=/opt/nifi
```
- A symlink refer to the new path for backward compatibility:
```
-docker run --rm --entrypoint /bin/bash apache/nifi:1.8.0 -c 'readlink /opt/nifi/nifi-1.8.0' /opt/nifi/nifi-current
+docker run --rm --entrypoint /bin/bash apache/nifi:1.12.0 -c 'readlink /opt/nifi/nifi-1.12.0' /opt/nifi/nifi-current
```
# Docker Image Quickstart
