Doc/Howto: more structure, more info on tuning proto params

docs/introduction/howto.rst

@@ -221,8 +221,8 @@ To interact with your node, read the doc of clients:
 
 And read :ref:`this page<alphanet>` to get alphanet tezzies.
 
-Run the node in a sandbox
+Use sandboxed mode
--------------------------
+------------------
 
 To run a ‘localhost-only’ instance of a Tezos network, we provide two
 helper scripts:
@@ -230,6 +230,9 @@ helper scripts:
 -  ``./src/bin_node/tezos-sandboxed-node.sh``
 -  ``./src/bin_client/tezos-init-sandboxed-client.sh``
 
+Run a sandboxed node
+~~~~~~~~~~~~~~~~~~~~
+
 For instance, if you want to run local network with two nodes, in a
 first terminal, the following command will initialize a node listening
 for peers on port ``19731`` and listening for RPC on port ``18731``.
@@ -258,6 +261,9 @@ command instead:
 
     ./src/bin_node/tezos-sandboxed-node.sh 1 --connections 0
 
+Use the sandboxed client
+~~~~~~~~~~~~~~~~~~~~~~~~
+
 Once your node(s) is/are running, open a new terminal and initialize the
 “sandboxed” client data:
 
@@ -289,6 +295,15 @@ activating the whole network. For instance:
     $ tezos-client rpc call blocks/head/protocol
     { "protocol": "ProtoALphaALphaALphaALphaALphaALphaALphaALphaDdp3zK" }
 
+Tune protocol alpha parameters
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``tezos-active-alpha`` alias use parameters from
+``scripts/protocol_parameters.json`` to activate protocol alpha. It can
+be useful to tune these parameters when you need to debug something,
+for example, change the number of blocks per cycle, the time between
+blocks, etc.
+
 Configuration options
 ---------------------