[Docs] Add Copyright information.

[mzr1996]

Modification

Add Copyright information. Refers to open-mmlab/mmcv#1181

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Merging #413 (fc1bd28) into master (5c4da16) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #413   +/-   ##
=======================================
  Coverage   76.68%   76.68%           
=======================================
  Files          97       97           
  Lines        5216     5216           
  Branches      853      853           
=======================================
  Hits         4000     4000           
  Misses       1096     1096           
  Partials      120      120           

Flag	Coverage Δ
unittests	76.68% <ø> (ø)

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

Impacted Files	Coverage Δ
mmcls/__init__.py	89.65% <ø> (ø)
mmcls/apis/__init__.py	100.00% <ø> (ø)
mmcls/apis/inference.py	20.00% <ø> (ø)
mmcls/apis/test.py	24.13% <ø> (ø)
mmcls/apis/train.py	22.72% <ø> (ø)
mmcls/core/__init__.py	100.00% <ø> (ø)
mmcls/core/evaluation/__init__.py	100.00% <ø> (ø)
mmcls/core/evaluation/eval_hooks.py	22.41% <ø> (ø)
mmcls/core/evaluation/eval_metrics.py	80.76% <ø> (ø)
mmcls/core/evaluation/mean_ap.py	100.00% <ø> (ø)
... and 87 more

---

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[Ezra-Yu]

LGTM