Add note about validity of opened ptrs after put

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/doc/extensions/experimental/sycl_ext_oneapi_inter_process_communication.asciidoc

@@ -207,6 +207,11 @@ with the handle have been deallocated, i.e. through a call to the `put` function
 or through freeing the USM device memory, the handle data is invalid and using
 it in the `put` and `open` functions will result in undefined behavior.
 
+[_Note:_ Any pointers retrieved through a call to the `open` function in any
+process on the system will still be valid and must still be freed through calls
+to the `close` function.
+_{endnote}_]
+
 !====
 a!
 [source]