Add build instructions to README

Author: jonnew

.bonsai/build-and-run.png

@@ -6,3 +6,17 @@ Acquisition System](https://open-ephys.github.io/onix-docs).
 - Library documentation: https://open-ephys.github.io/onix1-bonsai-docs
 - Hardware documentation: https://open-ephys.github.io/onix-docs
 
+### Run in visual studio
+1. Double click the `Setup.cmd` file in the `.bonsai` folder. This will install a
+   portable version of Bonsai in the `.bonsai` folder along with the Bonsai packages
+   required to compile and run the library.
+1. Open `OpenEphys.Onix1.sln` in Visual Studio (Community Edition is fine).
+1. Select which project to compile and run Bonsai against.
+   - `OpenEphys.Onix1`: core library
+   - `OpenEphys.Onix1.Design`: core library and GUI elements
+1. Press the Play button to
+   - Compile the library
+   - Run the Bonsai application installed in step 1
+   - Instruct Bonsai to load the compiled library
+
+![Select which library to compile](./.bonsai/build-and-run.png)