Fix formatting of config values in documentation

[Denton-L]

Currently, in our config documentation, there are many inconsistencies with the way values are being marked up. This patch is a very small start but we should try to go through all of the config/*.txt files and mark up config values with surrounding backticks. This way, it'll be obvious that these are special values that a user should pay attention to.

In particular, true and false are major offenders for not being surrounded by backticks.