documentation : somewhat ambiguous example of using nesting in a fluid grid system

[linstantnoodles]

http://twitter.github.com/bootstrap/scaffolding.html#fluidGridSystem

"Nesting with fluid grids is a bit different: the number of nested columns should not match the parent's number of columns. Instead, each level of nested columns are reset because each row takes up 100% of the parent column."

The example provided in the docs uses 12 as the number of columns in the top level, but that can lead to confusion because the number of nested columns actually does match up to the parents number of columns. A better example would be to use 10 as the number of top level columns, and then a pair of size 6 nested columns.

[cvrebert]

Duplicate of #5458