Added note about conflicting sshd promises

Ticket: ENT-13797
Signed-off-by: Lars Erik Wik <lars.erik.wik@northern.tech>

Author: larsewi

promise-types/sshd/README.md

@@ -16,6 +16,12 @@ Each promise manages a single directive in the drop-in config file.
 4. **Service restart** — restarts sshd if configuration was changed and the service is already running
 5. **Verification** — verifies the desired directive appears in the effective sshd config (`sshd -T`)
 
+## Conflicting promisers
+Having multiple promises with the same sshd keyword is not recommended.
+In case of conflicting promisers, the agent will attempt to converge the correct state for each one in the order they are evaluated.
+This means the last promise wins and determines the final value in the configuration file.
+It will also cause multiple restarts of the sshd service, which may be disruptive.
+
 ## What the module does NOT do
 - Install sshd — that is a `packages:` promise
 - Ensure sshd is running — that is a `services:` promise