Incorrect link to the mentioned book in the README.rst file

[roden]

Description

The link to the mentioned book seem to be incorrect at the end of the file https://github.com/dmlc/gluon-nlp/blob/v0.10.x/README.rst

Should probably be https://d2l.ai/d2l-en.pdf but is http://en.diveintodeeplearning.org/

[Sheng Zha]

@realBjornRoden many thanks for letting us know. I fixed the link just now and will port the fix to other release branches.

[Xingjian Shi]

Close because it has been fixed in the v0.x branch.