Mention serverSpawn and flowControl

remote-release-notes/v1_55.md

@@ -6,6 +6,8 @@
 
 Last month for terminal processes in local windows started launching in a new isolated process called the "pty host", isolating the important main process from potential native crashes and freeing up cycles in its important event loop. This release sees these changes come to remote terminals as well, sharing the majority of their implementation and bringing the hardening benefits of the pty host to remote.
 
+This also saw the departure of the `terminal.integrated.serverSpawn` and `terminal.integrated.flowControl` settings which are now stable and always on.
+
 ## Containers (version 0.163.x)
 
 ## WSL