Update Readme.md quickstart example

[loratera]

https://github.com/launchbadge/sqlx/#quickstart

shows an old library version which is not compatible with current tokio runtime, an update would be nice and a more elaborated quickstart example for the tokio runtime, since the tokio runtime is mentioned in the example and commented out. Something like this would be better in my opinion:

[dependencies]
sqlx = { version = "0.5", features = [ "postgres" ] }
async-std = { version = "1.9", features = [ "attributes" ] }

# or for tokio runtime
# sqlx = { version = "0.5", features = [ "runtime-tokio-rustls" , "postgres" ] }
# tokio = { version = "1", features = ["full"] }

also I saw from a pull request #1479 that the async-std runtime is not on by default, so it even has to be like this (but untested):

[dependencies]
sqlx = { version = "0.5", features = [ "runtime-async-std-native-tls", "postgres" ] }
async-std = { version = "1.9", features = [ "attributes" ] }

# or for tokio runtime
# sqlx = { version = "0.5", features = [ "runtime-tokio-rustls" , "postgres" ] }
# tokio = { version = "1", features = ["full"] }

[acro5piano]

@loratera Thanks, you saved my day!