nethsm-pkcs11: Improve documentation of keepalive

nethsm/pkcs11-setup.rst

@@ -111,11 +111,14 @@ The configuration is yaml-formatted:
           # it is possible to configure idle connections to make use of TCP keepalives, preventing the closing of connections by a firewall or detecting such cases
           tcp_keepalive:
             # the number of seconds before keepalives packets start being sent
+            # Corresponds to `TCP_KEEPALIVE` on macOS, `TCP_KEEPIDLE` on Linux, and the keepalivetime field of tcp_keepalive on Windows
             time_seconds: 600
             # the number of seconds between each keepalive packet
+            # Corresponds to `TCP_KEEPINTVL` on Linux and macOs, and keepaliveinterval field of tcp_keepalive on windows
             interval_seconds: 60
             # the number of keepalive packets being sent without a response before the connection 
             # is considered closed
+            # Corresponds to `TCP_KEEPCNT` on Linux and macOs, and is not used on Windows
             retries: 3
           # Time a connection can spend idle before being closed
           connections_max_idle_duration: 1800