Create README.md

README.md

+Universe
+========
+
+Getting started
+
+  git clone git@github.com:aspnet/Universe.git
+  cd Universe
+  build
+
+The default build will clone all known repos as subfolders. The clone will be the dev branch.
+
+If the build is run subsequently it will `git pull` the dev branch rather than clone. Note! This will cause a 
+merge if you have local changes. We may tweak how this is done if it causes problems.
+
+After folders are up to date, `build.cmd compile` is executed in each of the enlisted subfolders.
+
+If there are errors the build will continue with the next repo. 
+
+The last output is a list of which repos succeeded or failed.
+
+## build targets
+
+`build pull` will only clone or pull all repos.
+
+`build compile` this is the default target, described above.
+
+`build install` works like build compile, but will run `build.cmd install` in each subfolder. This means 
+any nupkg produced by the repo are copied into the local `.nuget` folder to be picked up by subsequent 
+repositories. The subfolders are built in dependency order.
+