[Docs] Add version for torchvision to avoide error.

[PeterH0323]

Motivation

I follow the doc to install the mmcls,

and I got the error:

segment fault

I look for which library to cause it then I found is import torchvision. So I look for the answer on the web and I found the answer: set the version of it.

Modification

Add version for torchvision in the installation of the doc. The version is according to the Pytorch official website V1.10.0

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.

[PeterH0323]

Hi @mzr1996 , pls take a look 😄

[PeterH0323]

Hi @Ezra-Yu , pls take a look 😄