I once read an article that talked about recording a solo classical
guitar.

The engineer who wrote the article said that he used a "mid-side"
microphone arrangement to get the most natural stereo image from the
solo guitar. (I hope I am recalling the terminology correctly here.)

What is this technique, and what microphones are most recommended?

I am going to be recording a solo steel-string acoustic guitar, and I
want to get as much of an ambient feel as I can.

Many thanks in advance....

*andy*