fixed cross-reference to corpus reader API docs, resolves https://github.com/nltk/nltk.github.com/pull/3 https://github.com/nltk/nltk.github.com/issues/2
fixed cross-reference to corpus reader API docs, resolves https://github.com/nltk/nltk.github.com/pull/3 https://github.com/nltk/nltk.github.com/issues/2

nltk/nltk,nltk/nltk,nltk/nltk