Add CONTRIBUTING

CONTRIBUTING.md

@@ -0,0 +1,40 @@
+# Contributing
+
+There are many ways to contribute to Route 0.  If you are an expert in
+networking, you can look for and correct errors, improve the existing lessons,
+add new lessons, or add IPv6 support.  Another way to contribute is to simply
+add new scenarios or topologies that you feel would be interesting for others.
+
+## Adding a new topology
+
+Adding a new topology is straightforward.
+
+1. Create a new directory in the `topology` directory.
+2. Create a `topo.py` file and define a class `NetTopo` that inherits from
+   `mininet.topo.Topo` and build your new topology in its constructor.
+3. Create a `zebra` directory and populate it with configuration files for the
+   `zebra` daemon to configure the interfaces in your topology.
+4. Create a `staticd` directory and populate it with configuration files for
+   the `staticd` daemon to configure the default routes on hosts.
+5. Create a `README.md` file to describe your topology.
+
+The easiest way to start would be to copy some other topology and customise it
+as appropriate.  Once ready, the topology should be automatically detected by
+`route-0.py` when you pass your topology's name as the `--topology` argument.
+
+## Adding a new scenario
+
+By default all topologies support the `plain` and `basic` scenarios.  Adding a
+additional scenarios is also pretty straightforward.
+
+1. In the topology's directory, make sure there is a `scenario` directory.
+   Create one if it doesn't exist.
+2. In the `scenario` directory create a new directory for your specific
+   scenario.
+3. In your new directory create one directory for each daemon you intend to
+   run.  You don't need to do this for `zebra` or `staticd` unless you want to
+   override the topology defaults.
+   
+Just like with the topology, the main script should automatically pick up the
+new scenario.
+