Added Qt crash course file (mostly empty)

doc/source/qtcrashcourse.rst

+Qt Crash Course
+===============
+
+Pyqtgraph makes extensive use of Qt for generating nearly all of its visual output and interfaces. Qt's documentation is very well written and we encourage all pyqtgraph developers to familiarize themselves with it. The purpose of this section is to provide an introduction to programming with Qt (using either PyQt or PySide) for the pyqtgraph developer.
+
+
+QWidgets and Layouts
+--------------------
+
+Signals, Slots, and Events
+--------------------------
+
+
+GraphicsView and GraphicsItems
+------------------------------
+
+
+Coordinate Systems
+------------------
+
+
+Mouse and Keyboard Input
+------------------------
+
+
+QTimer, the Event Loop, and Multi-Threading
+-------------------------------------------
+