Fixes #1051

```python -mflask``` is fine as is, but I think ```python -m flask``` is clearer to the reader.

I'd suggest that the script info paragraph be re-written too - it feels stilted and redundant as is. I'm not comfortable enough with the material to attempt to clear it up without fear of losing meaning/specifics though.

apologies to armin or kenneth if doc fixing PRs are an annoyance, trying to procrastinate exam study! :)