Documentation update: .svg file images are cropped in new graphiv version

[wittregr]

The current version of graphviz included in the Ubuntu 20.04 distribution (graphviz 2.42.2-3build2) generates .svg files that partially crop the image. The issue is with the default monitor dpi (dots-per-inch) used in the new version. Ubuntu and Windows assume a monitor dpi of 96.

The fix/workaround is to code the dpi into the dot command by adding the option -Gdpi=96. So a conversion from a example.out file to a example.svg file now looks like:

dot -Tsvg -Gdpi=96 example.out -oexample.svg

These edits can be done in the chemkin.sh and refinevisualization.sh scripts.
While the current graphviz version on Caviness does not have this issue we may need to address this at some point if/when graphiz versions are updated.

This should be added to the documentation.