Improve installation instructions

- Add separate `requrements_gae.txt` so that unnecessary
packages won't get installed on GAE. E.g., the production
environment already has lxml, jinja and markup packages
pre-installed, so no need to upload them to the server;
- Verbose output in runtime for setting Readability token
and Google tracking ID; therefore, don't submit fake values
in app/.env;
- Improve installation instructions in README.md;
- Increment minor version number.