[0.x] Update doc

[szha]

Description

Update doc after mx 1.7.

Checklist

Essentials

• [x] PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• [x] Changes are complete (i.e. I finished coding on this PR)
• [x] All changes have test coverage
• [x] Code is well-documented

Changes

• [x] Update doc after mx 1.7.

cc @dmlc/gluon-nlp-team

[leezu]

Why 3.8? People may be using the code with 3.6 already and it may break them?

[szha]

OK I will stay with 3.6. 3.5 seems too old.

[leezu]

Note that MXNet 1.6 pip wheels is incompatible with Horovod https://github.com/horovod/horovod/issues/2425

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/aa1d0fea3da17af389d1b3e3363c158639629d8a/index.html

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/8af0425f71de7aca094eb19652331b1fa374c48e/index.html

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/3eec988eb05ad07d538b43710032e73f4ac4eaff/index.html

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/cc161fcfeeeb8994fff6db1afa0893a7ca1e63be/index.html

[codecov[bot]]

Codecov Report

Merging #1521 (21f7995) into v0.x (48a2a96) will not change coverage. The diff coverage is 0.00%.

@@           Coverage Diff           @@
##             v0.x    #1521   +/-   ##
=======================================
  Coverage   33.44%   33.44%           
=======================================
  Files         155      155           
  Lines       15206    15206           
=======================================
  Hits         5086     5086           
  Misses      10120    10120           

Impacted Files	Coverage Δ
scripts/parsing/parser/biaffine_parser.py	0.00% <0.00%> (ø)

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/096592eadbd32a9a4889466a3a7f01458c7297bf/index.html

[github-actions[bot]]

The documentation website for preview: http://gluon-nlp-staging.s3-accelerate.dualstack.amazonaws.com/PR1521/21f7995732a37cd78a408cbb0b32e12e3cb4e423/index.html