Add documentation url to Cargo.toml

Cargo.toml

@@ -1,12 +1,13 @@
 [package]
-name        = "mongo_driver"
-version     = "0.2.0"
-authors     = ["Thijs Cadier <thijs@appsignal.com>"]
-description = "Mongo Rust driver built on top of the Mongo C driver"
-readme      = "README.md"
-repository  = "https://github.com/thijsc/mongo-rust-driver"
-keywords    = ["mongodb", "database"]
-license     = "MIT/Apache-2.0"
+name          = "mongo_driver"
+version       = "0.2.0"
+authors       = ["Thijs Cadier <thijs@appsignal.com>"]
+description   = "Mongo Rust driver built on top of the Mongo C driver"
+readme        = "README.md"
+documentation = "http://thijsc.github.io/mongo-rust-driver/mongo_driver/"
+repository    = "https://github.com/thijsc/mongo-rust-driver"
+keywords      = ["mongodb", "database"]
+license       = "MIT/Apache-2.0"
 
 [[test]]
 name = "tests"