Modify SurrealDB example a tad

[Dhghomon]

Hi,

Had a look over the SurrealDB example here which works well, I thought I'd make a few slight modifications:

• Note that it will look for the OPENAI_API_KEY env var
• Specify that the .user() part isn't to enable authentication but to authenticate (requiring authentication was made the default setting in 2.0 so the --unauthenticated flag is now used to opt out as opposed to before when it needed a flag to opt in)
• I see that anyhow is in Cargo.toml so might as well use it and add some question mark operator where the compiler doesn't complain about thread safety.

Also just a heads up that the docs link in https://crates.io/crates/langchain-rust seems to be dead, should it be https://docs.rs/langchain-rust/latest/langchain_rust/ instead?