Undocumented dependencies in text classification example

Text classification example depends on sentencepiece and subword_nmt packages. These should be documented in the README for the example.

[harshbafna]

@fbbradheintz This looks like some issue with the conda package for TorchText

conda doesn’t install sentencepiece as dependency for torchtext :

ubuntu@ip-172-31-22-66:~$ conda install torchtext -c pytorch
Solving environment: done


==> WARNING: A newer version of conda exists. <==
  current version: 4.5.12
  latest version: 4.8.2

Please update conda by running

    $ conda update -n base -c defaults conda

## Package Plan ##

  environment location: /home/ubuntu/anaconda3

  added / updated specs: 
    - torchtext

The following packages will be downloaded:

    package                    |            build
    ---------------------------|-----------------
    torchtext-0.5.0            |             py_1         1.4 MB  pytorch

The following NEW packages will be INSTALLED:

    cudatoolkit: 10.1.243-h6bb024c_0                          
    ninja:       1.9.0-py36hfd86e86_0                         
    pytorch:     1.4.0-py3.6_cuda10.1.243_cudnn7.6.3_0 pytorch
    torchtext:   0.5.0-py_1                            pytorch
    tqdm:        4.42.1-py_0                                  

Proceed ([y]/n)? n

Doing pip show torchtext after installing torchtext with conda lists sentencepiece as requirement :

ubuntu@ip-172-31-22-66:~$ pip show torchtext
Name: torchtext
Version: 0.5.0
Summary: Text utilities and datasets for PyTorch
Home-page: https://github.com/pytorch/text
Author: PyTorch core devs and James Bradbury
Author-email: [e-mail]
License: BSD
Location: /home/ubuntu/anaconda3/lib/python3.6/site-packages
Requires: tqdm, requests, torch, numpy, six, sentencepiece
Required-by: 
ubuntu@ip-172-31-22-66:~$ 

Directly installing torchtext through pip command installs sentencepiece as dependency

ubuntu@ip-172-31-22-66:~$ pip install torchtext
Collecting torchtext
  Downloading https://files.pythonhosted.org/packages/79/ef/54b8da26f37787f5c670ae2199329e7dccf195c060b25628d99e587dac51/torchtext-0.5.0-py3-none-any.whl (73kB)
     |████████████████████████████████| 81kB 8.3MB/s 
Requirement already satisfied: six in ./anaconda3/lib/python3.6/site-packages (from torchtext) (1.14.0)
Collecting torch
  Downloading https://files.pythonhosted.org/packages/24/19/4804aea17cd136f1705a5e98a00618cb8f6ccc375ad8bfa437408e09d058/torch-1.4.0-cp36-cp36m-manylinux1_x86_64.whl (753.4MB)
     |████████████████████████████████| 753.4MB 6.1kB/s 
Collecting sentencepiece
  Downloading https://files.pythonhosted.org/packages/74/f4/2d5214cbf13d06e7cb2c20d84115ca25b53ea76fa1f0ade0e3c9749de214/sentencepiece-0.1.85-cp36-cp36m-manylinux1_x86_64.whl (1.0MB)
     |████████████████████████████████| 1.0MB 37.9MB/s 
Requirement already satisfied: requests in ./anaconda3/lib/python3.6/site-packages (from torchtext) (2.20.0)
Collecting tqdm
  Downloading https://files.pythonhosted.org/packages/47/55/fd9170ba08a1a64a18a7f8a18f088037316f2a41be04d2fe6ece5a653e8f/tqdm-4.43.0-py2.py3-none-any.whl (59kB)
     |████████████████████████████████| 61kB 152kB/s 
Requirement already satisfied: numpy in ./anaconda3/lib/python3.6/site-packages (from torchtext) (1.16.4)
Requirement already satisfied: chardet<3.1.0,>=3.0.2 in ./anaconda3/lib/python3.6/site-packages (from requests->torchtext) (3.0.4)
Requirement already satisfied: urllib3<1.25,>=1.21.1 in ./anaconda3/lib/python3.6/site-packages (from requests->torchtext) (1.23)
Requirement already satisfied: idna<2.8,>=2.5 in ./anaconda3/lib/python3.6/site-packages (from requests->torchtext) (2.7)
Requirement already satisfied: certifi>=2017.4.17 in ./anaconda3/lib/python3.6/site-packages (from requests->torchtext) (2019.11.28)
Installing collected packages: torch, sentencepiece, tqdm, torchtext
Successfully installed sentencepiece-0.1.85 torch-1.4.0 torchtext-0.5.0 tqdm-4.43.0

[fbbradheintz]

FIxed in docs.

NB: It looks like sentencepiece is a dependency, but subword_nmt is not (at least in the latest version of torchtext).