How to indicate "Our remark"?

You could use square brackets

"Before the Greeks, the ancient Egyptians used it [the Golden Section] in the construction of their great pyramids."

I've also seen quotes like

"Before the Greeks, the ancient Egyptians used [the Golden Section] in the construction of their great pyramids."

I see this often in newspapers. In academic writing you also see [] as an insertion into a quote that is clearly not a part of the quote. For instance, the use of [sic!] to denote that a quote contains an error, but the error is not made by the one who uses the quote, but by the quote's original author.

"There was no resemblence [sic!] with the real thing."