Add information to the README about how to test the website locally

Author: giordano

README.md

@@ -1 +1,39 @@
 # https://juliaparallel.org
+
+## For contributors
+
+Clone the repository and `cd` to the new directory. Edit the files as you need.  To test the
+website locally, start julia with `julia --project` and do
+
+```julia
+julia> import Pkg
+
+julia> Pkg.instantiate()
+
+julia> import Xranklin
+
+julia> Xranklin.serve()
+  Activating project at `~/repo/juliaparallel.github.io`
+[ Info: 📓 de-serializing global context...
+[ Info: ⌛ processing config.md
+[ Info: ... [config.md] ✔ (δt = 2.1s)
+[ Info: 📓 de-serializing 0 local contexts...
+[ Info: 💡 de-serialization done (δt = 2.7s)
+
+[ Info: 💡 starting the full pass
+
+[ Info: > Full Pass [MD/1]
+[ Info: > Full Pass [MD/I]
+[ Info: > Full Pass [MD/2]
+[ Info: > Full Pass [O]
+[ Info: 🧵 loop (n=1) over 121 items
+
+[ Info: 💡 full pass done (δt = 5.9s)
+
+[ Info: Listening on: 127.0.0.1:8000
+✓ LiveServer listening on http://localhost:8000/ ...
+  (use CTRL+C to shut down)
+```
+
+Navigate to `localhost:8000` in a browser and you should see a preview of any modifications
+you make locally.