Mention prerequisites for running tutorial basing on observations

[noqqaqq]

Fixes #1993

Description

Issues were observed executing Text classification with the torchtext library tutorial.
To mitigate it, especially in Google Collab environment, prerequisite for installing proper version of portalocker library is needed.
Added this prerequisite to tutorial description.

Checklist

• The issue that is being fixed is referred in the description (see above "Fixes #ISSUE_NUMBER")
• Only one issue is addressed in this pull request
• Labels from the issue that this PR is fixing are added to this pull request
• No unnecessary issues are included into this pull request.

cc @pytorch/team-text-core @Nayef211

[pytorch-bot]

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[Nayef211]

LGTM!