Add pytorch td3 doc

[irisliucy]

Update TD3 documentation with PyTorch version. It includes updates in table, examples, benchmarks etc.

[irisliucy]

@Mergifyio rebase

[mergify[bot]]

Command rebase: success

Branch already up to date

[codecov[bot]]

Codecov Report

Merging #2174 (87cbe96) into master (7f25c98) will increase coverage by 0.17%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2174      +/-   ##
==========================================
+ Coverage   91.34%   91.51%   +0.17%     
==========================================
  Files         198      197       -1     
  Lines       10964    10929      -35     
  Branches     1392     1387       -5     
==========================================
- Hits        10015    10002      -13     
+ Misses        688      669      -19     
+ Partials      261      258       -3     

Impacted Files	Coverage Δ
src/garage/tf/_functions.py	55.12% <0.00%> (-13.73%)	:arrow_down:
src/garage/np/algos/cma_es.py	96.92% <0.00%> (-3.08%)	:arrow_down:
src/garage/np/algos/cem.py	97.43% <0.00%> (-2.57%)	:arrow_down:
src/garage/sampler/multiprocessing_sampler.py	89.61% <0.00%> (-1.30%)	:arrow_down:
src/garage/np/policies/fixed_policy.py	93.54% <0.00%> (-0.40%)	:arrow_down:
src/garage/torch/algos/pearl.py	48.29% <0.00%> (-0.18%)	:arrow_down:
src/garage/torch/algos/maml.py	98.12% <0.00%> (-0.06%)	:arrow_down:
src/garage/_functions.py	98.09% <0.00%> (-0.04%)	:arrow_down:
src/garage/tf/algos/rl2.py	95.41% <0.00%> (-0.04%)	:arrow_down:
src/garage/tf/algos/te.py	100.00% <0.00%> (ø)
... and 12 more

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