Update README.md

Fix typo
Fix inner attribute syntax from `#[foo];` to `#![foo]`

From the 0.10 changelog:
 * The inner attribute syntax has changed from `#[foo];` to `#![foo]`.
Add stdlib docs to the Linux binary tarball.

These are not installed anywhere, but are included under `./doc` for
those who want an offline copy with their nightlies. This increases the
size of the (compressed) tarball from 76 to 83 MB.
syntax: remove obsolete mutability from ExprVec and ExprRepeat.
std: TrieSet should implement container::{,Mutable}Set
extra: Add with_capacity to PriorityQueue and SmallIntMap
Register new snapshots
Added grow_fn and retain to Vec
Test fixes from rollup
auto merge of #13326 : alexcrichton/rust/rollup, r=alexcrichton

Closes #13313 (Fix typo in README.md)
Closes #13311 (Fix inner attribute syntax from `#[foo];` to `#![foo]`)
Closes #13309 (Add stdlib docs to the Linux binary tarball.)
Closes #13308 (syntax: remove obsolete mutability from ExprVec and ExprRepeat.)
Closes #13306 (TrieSet should impl Set/MutableSet; add with_capacity to PriorityQueue/SmallIntMap)
Closes #13303 (Register new snapshots)
Closes #13274 (Added grow_fn and retain to Vec)

*Issues Closed*

Closes #13249