readme: update

Remove the crates.io badge from the readme.
Installing clippy via crates.io is deprecated and rustup should be used instead, thus we should not promote crates.io here.

Don't have the entire clippy::correctness line in bold letters, I think it looks a little off.

README.md

@@ -2,7 +2,6 @@
 
 [![Build Status](https://travis-ci.com/rust-lang/rust-clippy.svg?branch=master)](https://travis-ci.com/rust-lang/rust-clippy)
 [![Windows Build status](https://ci.appveyor.com/api/projects/status/id677xpw1dguo7iw?svg=true)](https://ci.appveyor.com/project/rust-lang-libs/rust-clippy)
-[![Current Version](https://meritbadge.herokuapp.com/clippy)](https://crates.io/crates/clippy)
 [![License: MIT/Apache-2.0](https://img.shields.io/crates/l/clippy.svg)](#license)
 
 A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
@@ -12,7 +11,7 @@ A collection of lints to catch common mistakes and improve your [Rust](https://g
 We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
 
 * `clippy::all` (everything that is on by default: all the categories below except for `nursery`, `pedantic`, and `cargo`)
-* **`clippy::correctness`** (code that is just outright wrong or very very useless, causes hard errors by default)
+* `clippy::correctness` (code that is just **outright wrong** or **very very useless**, causes hard errors by default)
 * `clippy::style` (code that should be written in a more idiomatic way)
 * `clippy::complexity` (code that does something simple but in a complex way)
 * `clippy::perf` (code that can be written in a faster way)