Adding new plugin – where to insert readme.txt ?

Hello, the problem is not with existing plugin, my problem is with plugin upload..
I’m from russia and i don’t understand english very good.

So the problem is that i have uploaded plugin (in development center) and they replyed to me that i don’t have readme.txt

I have created one but i don’t know where to upload it.

Should it be in plugins folder or in zip ?? where to upload it ?

(for modirators: feel free to move my post in right topic/category)