unordered list bullets and trailing whitespace

[mwunderl]

Issue #, if available: 18

Description of changes:
standardize list formatting and remove excess whitespace

Instructions used

several markdown files in folders in the tuts directory use • character to mark list items, which is not supported by markdown. replace these with hyphens and check for other markdown formatting issues

update the instructions in instra/tutorial-gen/ to avoid these issues in the future

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[yanjieniu]

Approve.