[alertmanager-snmp-notifier] Update README with correct chart name

[FalkW]

As the name of the chart was changes an update in the README.md is required to reflect this change.

What this PR does / why we need it

So the user is able to install the chart by following the readme.

The current one is wrong:

helm install test  prometheus-community/snmp-notifier
Error: INSTALLATION FAILED: chart "snmp-notifier" matching  not found in prometheus-community index. (try 'helm repo update'): no chart name found

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])

[zeritti]

Thank you, @FalkW, for your PR. Please, raise the chart's version number in Chart.yaml.

[FalkW]

Thank you, @FalkW, for your PR. Please, raise the chart's version number in Chart.yaml.

Done.

[zeritti]

Please, check your commits' signatures - DCO check is not passing.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.