Add note about local executor and enforcing resource limits (#4468)

Signed-off-by: Ben Sherman <[email protected]>

docs/executor.md

@@ -328,6 +328,10 @@ The `local` executor is used by default. It runs the pipeline processes on the c
 
 The `local` executor is useful for developing and testing a pipeline script on your computer, before switching to a cluster or cloud environment with production data.
 
+:::{note}
+While the `local` executor limits the number of concurrent tasks based on requested vs available resources, it does not enforce task resource requests. In other words, it is possible for a local task to use more CPUs and memory than it requested, in which case it may starve other tasks. An exception to this behavior is when using {ref}`container-docker` or {ref}`container-podman` containers, in which case the resource requests are enforced by the container runtime.
+:::
+
 (lsf-executor)=
 
 ## LSF