Merge ~pelpsi/lp-signing:update-development-documentation into lp-signing:master

[Simone Pelosi]

Add register-client command to the documentation

[Guruprasad (lgp171188)]

LGTM 👍 Please address my review comment, squash the commits into a single logical commit with an appropriate commit message before merging this.

review: Approve

diff --git a/README.rst b/README.rst
index 5fc6b9b..8b40442 100644
--- a/README.rst
+++ b/README.rst
@@ -38,6 +38,21 @@ Generate another key pair, and add the private half to ``private_keys``
 
     $ env/bin/lp-signing generate-key-pair
 
+If you want to communicate with the ``lp-signing`` service via a client application, 
+you need a keypair for it. The keypair can be generated using 
+the ``env/bin/lp-signing generate-keypair`` command, which prints the public 
+and private keys of the generated keypair. 
+The public key from that output can be registered using the 
+``env/bin/lp-signing register-client <client-name> <client-public-key>`` command,
+where ``<client-public-key>`` is a base64-encoded NaCl public key,
+and the private key has to be used in the client application.
+Please check the example client code below in this document for more details.
+
+.. note::
+    In the case of the Launchpad development instance acting as a client, 
+    the keypair can be obtained from ``configs/development/launchpad-lazr.conf``
+    in the Launchpad repository and the public key registered using this command.
+
 Start the server::
 
     $ make run