docs: add devcontainer unstable testing instructions

website/docs/tutorials/upgrade.md

@@ -93,15 +93,19 @@ Dev Containers: Rebuild Without Cache and Reopen In Container
 
 ![Simple Card View](./assets/rebuild-without-cache.jpg)
 
-### When Using Geoprocessing Less Than 7.0
+### Unstable Testing
 
-The latest version of the `geoprocessing-workspace` will only work with geoprocessing 7.x projects. This is due to a change in how GDAL produces flatgeobuf files. If you suddenly see errors of `"Not a FlatGeobuf file"` when trying to read your file, this is likely the reason. In order to continue to develop older 6.x and lower geoprocessing projects you will need to start your devcontainer using the `local-dev-pre-7x` environment. This is pinned to an older version of the docker image - `seasketch/geoprocessing-workspace:sha-69bb889`
+If you are testing out a new `unstable` image you will need to pull using that tag instead:
+
+```bash
+docker pull seasketch/geoprocessing-workspace:unstable
+```
+
+Then, when restarting your VSCode devcontainer, choose the `unstable` version.
 
-If you're maintaining your own development environment then you should look to have at least the following versions at minimum:
+### When Using Geoprocessing Less Than 7.0
 
-- Node 20.12.1
-- NPM 10.5.0
-- GDAL 3.5.0
+The latest version of the `geoprocessing-workspace` will only work with geoprocessing 7.x projects. This is due to a change in how GDAL produces flatgeobuf files. If you suddenly see errors of `"Not a FlatGeobuf file"` when trying to read your file, this is likely the reason. In order to continue to develop older 6.x and lower geoprocessing projects you will need to start your devcontainer using the `local-dev-pre-7x` environment. This is pinned to an older version of the docker image - `seasketch/geoprocessing-workspace:sha-69bb889`
 
 ### Upgrade Windows Geoprocessing