fix build on OpenBSD

fs.go

@@ -1,4 +1,4 @@
-//go:build !windows
+//go:build !windows && !openbsd
 
 package main
 

fs_other.go

@@ -1,4 +1,4 @@
-//go:build windows
+//go:build windows || openbsd
 
 package main
 
@@ -12,9 +12,9 @@ import (
 var fsCmd = &cli.Command{
 	Name:                      "fs",
 	Usage:                     "mount a FUSE filesystem that exposes Nostr events as files.",
-	Description:               `doesn't work on Windows.`,
+	Description:               `doesn't work on Windows and OpenBSD.`,
 	DisableSliceFlagSeparator: true,
 	Action: func(ctx context.Context, c *cli.Command) error {
-		return fmt.Errorf("this doesn't work on Windows.")
+		return fmt.Errorf("this doesn't work on Windows and OpenBSD.")
 	},
 }