Improve project marketing

[pimeys]

When releasing 0.2, we should announce the project existence in certain medium, such as Reddit and Rust forums.

The README should gather bullet points of the goals of this crate.

• [x] announce project release
• [x] write about project goals in README

[pimeys]

https://www.reddit.com/r/rust/comments/8nze3p/announcing_a2_a_batteriesincluded_apple_push/