[DOC] Edit FAQ to add 30 series installation problem

[RyanXLi]

Resolves #4131 , resolves #4047 , resolves #4160

[codecov]

Codecov Report

Merging #4176 (243e77d) into master (63772c5) will decrease coverage by 0.27%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #4176      +/-   ##
==========================================
- Coverage   61.92%   61.64%   -0.28%     
==========================================
  Files         226      226              
  Lines       16852    16854       +2     
  Branches     2851     2852       +1     
==========================================
- Hits        10435    10390      -45     
- Misses       5895     5944      +49     
+ Partials      522      520       -2     

Flag	Coverage Δ
unittests	61.61% <33.33%> (-0.26%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet/apis/inference.py	19.54% <33.33%> (-0.46%)	⬇️
mmdet/models/roi_heads/mask_scoring_roi_head.py	55.35% <0.00%> (-32.15%)	⬇️
mmdet/models/roi_heads/test_mixins.py	45.73% <0.00%> (-8.53%)	⬇️
mmdet/models/roi_heads/mask_heads/maskiou_head.py	94.62% <0.00%> (-5.38%)	⬇️
mmdet/models/detectors/cornernet.py	94.87% <0.00%> (-5.13%)	⬇️
mmdet/models/dense_heads/corner_head.py	74.86% <0.00%> (-1.92%)	⬇️
mmdet/models/roi_heads/mask_heads/fcn_mask_head.py	70.55% <0.00%> (-1.23%)	⬇️

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