docs: describe updating process

Signed-off-by: Jan Kowalleck <[email protected]>

README.md

@@ -23,3 +23,18 @@ Install [`cyclonedx-gomod`](https://github.com/CycloneDX/cyclonedx-gomod?tab=rea
 ```shell
 brew install cyclonedx-gomod
 ```
+
+----
+
+## Updating
+
+### For consumers
+
+You found an outdated formula? Please let us know - open a github issue and request a bump:  
+<https://github.com/CycloneDX/homebrew-cyclonedx/issues/new>
+
+### For maintainers
+
+Formula updating is semi-automated.  
+Trigger it by dispatching the [github action "Update a formula"](https://github.com/CycloneDX/homebrew-cyclonedx/actions/workflows/update-formula.yml); this should result in a pull-request with the needed updates.  
+The PR is opened as bot, not as the dispatcher, so that the dispatcher/maintainer can review/approve/merge the PR as they like.