Add license and description

Cargo.toml

@@ -2,6 +2,8 @@
 name = "multiboot2"
 version = "0.1.0"
 authors = ["Philipp Oppermann <dev@phil-opp.com>"]
+license = "MIT/Apache-2.0"
+description = "An experimental Multiboot 2 crate for ELF-64 kernels."
 
 [dependencies.bitflags]
 version = "0.4.0"