* Clean up tutorial docs for installable app pattern
- reading sequentially through the tutorial works.
- fixes references to `export FLASK_APP=flaskr.flaskr`
* Fixes titles for each section of flaskr tutorial
* Revert grammar
* Emphasize the Packaging Guide
- adds more general packaging resource
- removes the emphasis put on setuptools
* rephrase and remove note admonitions
- expanded on few points
- removed note blocks, they are unneccessary
* Remove note about reinstalling to update cli
- I had mistakenly thought it was necessary to
re-install the app to update the cli.
- the `--editable` flag detects the change and
the cli updates without issue.
Kyle Lawlor