Add virtualenv support and info

[anargyri]

Description

Modifications required to support virtualenv which is an extension of venv but differs somewhat in installation.

• Tested installation and updated the SETUP and README documentation.
• Modified the dockerfile to support virtualenv and tested docker containers.

Related Issues

Checklist:

• I have followed the contribution guidelines and code style for this project.
• I have added tests covering my contributions.
• I have updated the documentation accordingly.
• This PR is being made to staging branch and not to main branch.

[miguelgfierro]

lgtm

[miguelgfierro]

after this is merged into staging, a new documentation job will be triggered. In the past I had problems when using pyspark and readthedocs. We should check if this causes a problem this time, FYI @YanZhangADS

[anargyri]

On a DSVM, compilation works and the docs look ok on Firefox Let's check on readthedocs too after the merge.

[codecov-commenter]

Codecov Report

Merging #1520 (31d36f2) into staging (c5029af) will decrease coverage by 12.28%.
The diff coverage is n/a.

❗ Current head 31d36f2 differs from pull request most recent head 0aca010. Consider uploading reports for the commit 0aca010 to get more accurate results

@@             Coverage Diff              @@
##           staging    #1520       +/-   ##
============================================
- Coverage    74.23%   61.95%   -12.29%     
============================================
  Files           84       84               
  Lines         8369     8369               
============================================
- Hits          6213     5185     -1028     
- Misses        2156     3184     +1028     

Impacted Files	Coverage Δ
...ecommenders/models/newsrec/io/mind_all_iterator.py	12.21% <0.00%> (-86.65%)	⬇️
recommenders/models/newsrec/io/mind_iterator.py	15.67% <0.00%> (-82.71%)	⬇️
...ommenders/models/deeprec/io/sequential_iterator.py	15.85% <0.00%> (-81.94%)	⬇️
recommenders/models/newsrec/models/base_model.py	30.90% <0.00%> (-59.40%)	⬇️
...deeprec/models/sequential/sequential_base_model.py	46.97% <0.00%> (-47.66%)	⬇️
recommenders/models/geoimc/geoimc_data.py	41.66% <0.00%> (-44.80%)	⬇️
...enders/models/deeprec/io/dkn_item2item_iterator.py	45.61% <0.00%> (-42.11%)	⬇️
...menders/models/deeprec/models/graphrec/lightgcn.py	51.47% <0.00%> (-40.24%)	⬇️
recommenders/datasets/mind.py	0.00% <0.00%> (-30.85%)	⬇️
recommenders/datasets/movielens.py	75.84% <0.00%> (-15.17%)	⬇️
... and 10 more

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