Update the introduction section

docs/source/tech_overview.rst

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+.. _a_tech_overview:
+
+******************
+Technical Overview
+******************
+
+
+novelWriter is built as a cross-platform application using `Python 3 <https://www.python.org/>`_ as
+the programming language, and `Qt 5 <https://www.qt.io/>`_ framework for the user interface.
+
+novelWriter is built for Linux first, so this is where it works best. However, it also runs fine
+on Windows and MacOS due to the cross-platform framework it's built on. The author of the
+application doesn't own a Mac, so on-going Mac support is dependent on user feedback and user
+contributions.
+
+Spell checking in novelWriter is provided by a third party library called
+`Enchant <https://abiword.github.io/enchant/>`_. Please see the section on :ref:`a_custom_dict` for
+how to install spell checking languages.
+
+For install instructions for novelWriter, see :ref:`a_started`.