[Grace-core] Updated documentation

[Kim Bruce]

In anticipation of students writing Grace programs I've updated the documentation that was made available for our first tutorial.  It is available at http://www.cs.pomona.edu/~kim/GraceStuff/ .  I'm also linking to it from the page on the text "Programming with Grace", which is at http://www.cs.pomona.edu/~kim/ProgrammingWithGrace/

Please let me know if you see any errors or have suggestions for improvements.

Kim