README: minor fixes to templatematch customisation section

Updates the README for clarity and completeness.

Notable changes:
* added list of valid values for `match_method`, which were missing
* update `confirm_method` formatting to emphasise they are strings
* changed to fixed-width font for parameter values
* using double-quotes to indicate strings
Merge pull request #1 from abaharna/templatematch-improvements

README: minor fixes to templatematch customisation section