merge: improve documentation of fbid dict used for merge bid
I improved the comments explaning what the dict contains meanwhile organizing
the comment structure which prevents some confusion.
Due to formatting issues, the empty dict was wrapped in `()` which might decieve
in thinking that it's a tuple of dict until you decide to find a comma.
Differential Revision: https://phab.mercurial-scm.org/D8818
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}