[Doc] Fix the broken link on the installation page

[TaoLv]

Description

This PR fixes the broken link for MXNet tuning guide on the installation page: https://mxnet.incubator.apache.org/versions/master/install/index.html?platform=Linux&language=Python&processor=CPU

Previously we used a relative link address ../../faq/perf.md#intel-cpu which is compiled to https://mxnet.incubator.apache.org/versions/faq/perf.md#intel-cpu missing master in it.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[TaoLv]

@pengzhao-intel @aaronmarkham Please review.

[pengzhao-intel]

LGTM

[aaronmarkham]

I'd really like to stay away from hard coding the urls. This makes previews hard to test - if you keep ending up on production instead of your preview.
You should be able to change this to ../faq/perf.md#intel-cpu.

[aaronmarkham]

Actually nevermind. This page is so messed up. The link should have been converted from .md to .html, but that didn't happen. Better to fix the link for now. We still have a bug on this page though - .md links should get converted to html so that you can browse this on github and on the website.