doc: fix installation cmd in release 1.8.2 blog

[shaowenchen]

• Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...) /kind documentation

• What this PR does / why we need it:

helm repo add volcano-sh https://volcano-sh.github.io/helm-chart

Error: looks like "https://volcano-sh.github.io/helm-chart" is not a valid chart repository or cannot be reached: failed to fetch https://volcano-sh.github.io/helm-chart/index.yaml : 404 Not Found

• Which issue(s) this PR fixes:

helm chart repo is https://volcano-sh.github.io/helm-charts ，not https://volcano-sh.github.io/helm-chart

[volcano-sh-bot]

Welcome @shaowenchen!

It looks like this is your first PR to volcano-sh/website 馃帀.

Thank you, and welcome to Volcano. :smiley:

[volcano-sh-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Thor-wl

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