Improve options section of the readme

[ArtskydJ]

• Clarify arrayMerge's arguments.
• Fix clone heading level.

[TehShrike]

Looks good to me. I wonder if those comments inside concatMerge should be assertion comments with the =>, just to guarantee they're correct?

[ArtskydJ]

Like this?

destinationArray // => [1, 2, 3]
sourceArray // => [3, 2, 1]
options // => { arrayMerge: concatMerge }

[TehShrike]

Yeah, that should do it I think.

[ArtskydJ]

Done.

[TehShrike]

Published as 1.3.1. Thanks!