Add non core testing DO point

Add testing: DO cover non-core code including build and view models.
Add test naming guideline

Add testing guideline: DO use clear and understandable naming of tests.
Shorten the introduction

Attempt to condense the introduction down to outlining the purpose of
the document and remove content summarising the "Simple Made Easy"
video.
Would envisage re-adding some of the general comments about software
development as a design activity, but would rather re-add smaller parts
at a time with more discussion.
Merge pull request #6 from danielrbradley/master

Two new testing points & much shorter introduction