docs: make it clear that database_path is a folder

conduit-example.toml

@@ -12,7 +12,7 @@
 #server_name = "your.server.name"
 
 # This is the only directory where Conduit will save its data
-database_path = "/var/lib/conduit/conduit.db"
+database_path = "/var/lib/conduit/"
 
 # The port Conduit will be running on. You need to set up a reverse proxy in
 # your web server (e.g. apache or nginx), so all requests to /_matrix on port