Postcolonialism can be seen as a philosophy, a reconsideration of history, or a method of cultural studies. In short, it's a field with its work cut out for it. For our purposes, we can think of postcolonial readers as those "concerned with literature produced by colonial powers and works produced by those who were/are colonized" (Source). The basic idea is to read between the lines of the stories written by history's winners and see what may have be left out. With "Rikki-Tikki-Tavi," what does the story leave out of its presentation of India? And once reincorporated into the story, does this ignored history change the way we perceive and find meaning in the story? Only one way to find out: we're going to have to shake things up a little.
Kipling snuck support for India into "Rikki-tikki-tavi" by giving the cobras motivations and feelings.
The story sees the cobras as evil not because of the postcolonial view we're proposing here but from of Rikki-tikki's youthful, immature life view. See "Coming of Age" for more.