docs(redis): Document port and unixSocket options

doc/redis.md

@@ -2,6 +2,21 @@
 
 [Redis](https://redis.io/) is an in-memory data structure store used as a database, cache, and message broker.
 
+## Unix socket
+
+Redis supports the usage of [Unix socket](https://man7.org/linux/man-pages/man2/socket.2.html) to listen to connections. By default, Redis listens to connections over TCP on port `6379`. When using Unix socket, you can decide to either enable listening on both or disable listening on TCP by setting port to `0` (recommended).
+
+```nix
+# Inside `process-compose.<name>`
+{
+  services.redis."r1" = {
+    enable = true;
+    port = 0;
+    # relative paths are relative to the data directory, which is `$PWD/data/r1` by default
+    unixSocket = "./redis.sock";
+  };
+}
+```
 ## Usage example
 
 <https://github.com/juspay/services-flake/blob/main/nix/services/redis_test.nix>