Added one tip and a section on importing packages to tricks_and_tips.md.

I was thinking about placing the section on multiple import packages towards the beginning when they are first introduced, but I think it'd be better left here. 

Please let me know if you'd like me to change the format of the section I added. I'm comfortable with the current format only because I haven't found anything else looks better. 

This pull request inspired me to write a blog post which describes each method with examples. I've included a link to the post in the section. To the best of my ability, you can be sure that the link will be valid for as long as possible. I'll remove or update the link accordingly if it changes or becomes unavailable. Thanks!