What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind bug

/kind task

/kind feature

What does this PR do / why do we need it:

Update cache document since we officially support caching over MindRecord dataset now.

Which issue(s) this PR fixes:

Fixes ##I49FP9:update cache doc

Special notes for your reviewers: