added 300 node lab (#36)

lab-topologies/300-node-lab/README.md

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+# README.md
+
+![topo](./topo.png)
+
+## What is it
+
+This lab topology has been created using a script available [here](https://github.com/rschmied/topogen).  
+It's big and random. Yeah!
+
+## Things to do
+- the DNS host should have access to the Internet to install dnsmasq and iptables. It will provide Internet access for the entire lab and also acts as the DNS.
+- name resolution for all routers is available, the server is the DNS host. All records point to the loopback addresses (e.g. things like `telnet r84` should work from everywhere).
+- all routers run OSPF in area 0 `¯\_(ツ)_/¯`
+- try some traceroute
+
+> **Note**: Obviously, this needs a ton of resources (and licenses) to run. It's mostly a proof of concept and a bit of a scale test demo topology. Check the `topogen` repository (link above) to create smaller topologies.
+