docs: Upgrading 4.0 docs

Signed-off-by: Alan Clucas <alan@clucas.org>

docs/upgrading.md

@@ -1,36 +1,21 @@
 # Upgrading Guide
 
+For the upgrading guide to a specific version of workflows change the documentation version in the lower right corner of your browser.
+
 Breaking changes  typically (sometimes we don't realise they are breaking) have "!" in the commit message, as per
 the [conventional commits](https://www.conventionalcommits.org/en/v1.0.0/#summary).
 
-## Upgrading to v3.7
-
-See also the list of [new features in 3.7](new-features.md).
-
-For upgrades to older versions of Argo Workflows, please change to the documentation for the version of interest.
+## Upgrading to v4.0
 
 ### Deprecations
 
-The following features are deprecated and will be removed in a future verison of Argo Workflows:
+Several features were marked for deprecation in 3.6, and are now removed:
 
-* The Python SDK is deprecated, we recommend migrating to [Hera](https://github.com/argoproj-labs/hera)
+* The Python SDK is removed, we recommend migrating to [Hera](https://github.com/argoproj-labs/hera)
 * `schedule` in CronWorkflows, `podPriority`, `mutex` and `semaphore` in Workflows and WorkflowTemplates.
 
 For more information on how to migrate these see [deprecations](deprecations.md)
 
-### Removed Docker Hub Image Publishing
-
-Pull Request [#14457](https://github.com/argoproj/argo-workflows/pull/14457) removed pushing to docker hub.
-Argo Workflows exclusively uses quay.io now.
-
-### Made Parameter Value Overriding Consistent
-
-Pull Request [#14462](https://github.com/argoproj/argo-workflows/pull/14462) made parameter value overriding consistent.
-This fix changes the priority in which the values are processed, meaning that a Workflow argument will now take priority.
-For more details see the example provided [here](https://github.com/argoproj/argo-workflows/issues/14426)
-
-## Upgrading to 4.0
-
 ### Logging levels
 
 The logging levels available have been reduced to `debug`, `info`, `warn` and `error`.
@@ -48,3 +33,17 @@ Use the following command to selectively apply the full CRDs for an existing ins
 ```bash
 kubectl apply --server-side --kustomize https://github.com/argoproj/argo-workflows/manifests/base/crds/full?ref=v4.0.0
 ```
+
+### Go language (Developers)
+
+If you are importing argo-workflows code into your go project you need to be aware of some changes.
+
+Many go-lang functions have changed signature to require a [context](https://pkg.go.dev/context) as the first parameter.
+In almost all cases you will need to provide a logger in your context.
+The details are in [logging.go](https://github.com/argoproj/argo-workflows/blob/main/util/logging/logging.go)
+
+In particular:
+
+* Your logger must conform to the logging interface `Logger` from that file.
+* Your logger should be retrievable from the context key `logger` (util/logging/logging.go `LoggerKey`)
+* You may wish to use the logger from [slog.go](https://github.com/argoproj/argo-workflows/blob/main/util/logging/logging.go)