Alamofire: Add guidance for logging in Usage.md or AdvancedUsage.md

[0xced]

• [x] I've read, understood, and done my best to follow the *CONTRIBUTING guidelines.

I was searching what was the best way to log Alamofire requests and responses and the first thing I found was How can I log each request/response using Alamofire? on Stack Overflow. But the answers were not very satisfactory.

I finally found this comment from @jshier. I think this should be included in either Usage.md or AdvancedUsage.md. Note that EventMonitor is not mentioned at all in those usage guides.

[jshier]

Yes, this will be addressed as part of the update to AdvancedUsage.

[jshier]

The Advanced Usage doc update is now available as #3057. You can read the EventMonitor section off the PR, though it is rather brief.