DOC: gpc/gpt: add commments of gpc/gpt array definitions on stick tables.

Some users misunderstood that the parameter of gpc() gpt()
store types on the table line presents the number of elements
of the array to store and not an index of gpt/gpc tag/counter.

This patch adds some explanations.

This patch addresses github issue #1630

It should be backorted in until branch 2.5.
1 file changed