Consider clarifying what `Trace: Server` does in the Readme file

[July541]

Currently, we only have Scroll down to Haskell › Trace: Server and set it to messages. in the Readme file, it's confusing what the message is and where the message is from.

Proposal:

1. Consider clarifying what Trace: Server does in the Readme file.
2. Consider changing to set it to debug, setting the trace to debug corresponding to hls's debug mode.