Update commands.md

More info about member and mirror nodes when setting up the keys.

content/pages/wiki/duniter/commands.md

@@ -18,6 +18,12 @@ sudo -u duniter <cmd>
 
 Lets you configure the cryptographic keychain used by your node. It is through this trousseau that your node can be identified and its answers authenticated, verified.
 
+Every duniter node has an cryptopraphic keys trousseau, used by sign their transmited information. There are two duniter node types:
+
+1. member nodes: whose keys trousseau match a membre's identity and it get involved in the blocks writting opperation.
+
+2. mirror nodes: when their keys trousseau don't match any member's identity. They can not write any block but they are useful for the network resilence and for answering the client requests.
+
 This keychain consists of a private key and a public key Ed25519.
 
     duniter wizard key