fix(tutorial1.org): typos and suggestions
fix(tutorial1.org): typos and suggestions

fpvandoorn/tutorial,Hodapp87/cs6460_project,avigad/tutorial,cjmazey/fork_leanprover_tutorial,Hodapp87/cs6460_project,leanprover/tutorial,soonhokong/lean-tutorial,leanprover/tutorial,fpvandoorn/tutorial,fpvandoorn/tutorial,cjmazey/fork_leanprover_tutorial,soonhokong/lean-tutorial,cjmazey/fork_leanprover_tutorial,avigad/tutorial,avigad/tutorial,soonhokong/lean-tutorial,leanprover/tutorial,Hodapp87/cs6460_project