Update release notes for 0.3.16 release #1870

Job	Run time
Build Benchmarks	1m 9s
Clippy	49s
Documentation	19s
Build Benchmarks (w/ yoga)	1m 30s
Rustfmt	16s
Markdown Lint	7s
Test Fixture Formatting	24s
Test Suite [Features: alloc]	3m 22s
Test Suite [Features: Default]	3m 12s
Test Suite [Features: std (no grid)]	3m 20s
Test Suite [Features: Default + serde]	3m 59s
Test Suite [Features: flexbox + std]	3m 22s
Test Suite [Features: grid + std]	3m 54s
Test Suite [Features: grid + alloc]	3m 20s
Test Suite [Features: Default] (Rust 1.65)	7m 57s
Test Suite [Features: std (no grid or flexbox)]	3m 6s
Test Suite [Features: None]	3m 50s
	43m 56s

Provide feedback