What is the purpose of this pull request? (put an "X" next to item)

[X] Documentation update #11963

What changes did you make? (Give an overview)

Removed an example that does not apply to this rule.

Removed writable flag as it's irrelevant for this rule.

Modified a 'write' example (b = 10) to 'read' example (var bar = a + 1).

Is there anything you'd like reviewers to focus on?

Should there be a 'correct' example like this:

/*global b*/
/*eslint no-undef: "error"*/
b = 10;

It is indeed a correct code for this rule, but it isn't the right way to use eslint global variables in general.