Add workbench developer document

dev-docs/source/Workbench.rst

+.. _Workbench:
+
+=====================
+Workbench Development
+=====================
+
+.. contents::
+  :local:
+
+
+Overview
+########
+
+The workbench is the new PyQt-based GUI that will be the primary interface for
+interacting with the mantid framework. The plotting is provided by
+`matplotlib <https://matplotlib.org/>`_. It will eventually replace MantidPlot.
+
+Building
+########
+
+The following build instructions assume you have follwed the instructions on the :ref:`GettingStarted` pages and can build mantid and MantidPlot. To enable the
+build of the workbench simply set the cmake flag ``ENABLE_WORKBENCH=ON`` and
+build as normal. A ``workbench`` startup script (Linux/macOS) or executable (Windows) will appear in the ``bin`` folder. For Windows the executable will appear in the configuration subdirectory of ``bin``.
+
+Packaging
+#########
+
+Packaging is currently only supported on Linux platforms and must be enabled
+using the cmake flag ``PACKAGE_WORKBENCH=ON``.

dev-docs/source/index.rst

@@ -208,5 +208,6 @@ Component Overviews
    MultiThreadingInAlgorithms
    PythonVSCppAlgorithms
    RemoteJobSubmissionAPI
+   Workbench
    WritingAnAlgorithm
    WritingCustomConvertToMDTransformation