README.md: remove DownloadAsync() example

[slook]

• Removed: "Download a file" section; it's not really needed here, nor is it a prime example of the library's capabilities
• Changed: Corrected a grammatical mistake in the "Search for something" section

Suggest a different function could be added here instead as a better example, such as responding to a search request or sending a chat message.

[jpdillingham]

Thanks. I think I'll strip all examples for now.

[slook]

It'll be good to steer the docs towards the library having the intent of making a fully-featured client rather than it being seen as a handy shortcut to make bare-bones partial implementation for some slop bot tool!

[jpdillingham]

I agree, I just can't spare the time to write them up. In the meantime if someone really wants they can spend the tokens to analyze the code :)