document limit-active-tasks strategy
concourse/concourse#4118
concourse/concourse#4148
concourse/concourse#4208
concourse/concourse#4277
concourse/concourse#4142
concourse/concourse#4221
concourse/concourse#4293
#### <sub><sup><a name="v550-note-1" href="#v550-note-1">:link:</a></sup></sub> feature
-We have changed our release notes flow! Now, contributors can add draft release notes right in their PRs, by modifying the `release-notes/latest.md` file in the `concourse/concourse` repo.
+There is a new [container placement strategy](https://concourse-ci.org/container-placement.html), `limit-active-tasks`. If you specify this strategy, the cluster will maintain a counter of the number of task containers currently running on each worker. Whenever it is time to run a new container, when this strategy is in use, the worker with the fewest active tasks containers will be chosen to run it.
+
+There is also an optional 'max active tasks per worker' configuration. If this is set to a positive integer, you will see the following behaviour: If all workers are at their active task limit, you will see the message `All workers are busy at the moment, please stand-by.` and the scheduler will re-try a minute later. This pattern will repeat each minute indefinitely, until a worker is available.
+
+Thanks to @aledeganopix4d for all their hard work on this feature! #4118, #4148, #4208, #4277, #4142, #4221, #4293
+
+#### <sub><sup><a name="v550-note-2" href="#v550-note-2">:link:</a></sup></sub> feature
+
+We have changed our release notes flow! Now, contributors can add draft release notes right in their PRs, by modifying the `release-notes/latest.md` file in the `concourse/concourse` repo #4312.
