[video_player]Update README.me

[trueshail]

• Reflecting the updating API for checking the controller is Initialized

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. You must list at least one issue.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Closes flutter/flutter#79178

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• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
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[trueshail]

@googlebot I signed it!

[stuartmorgan]

Thanks for the contribution! Could you please update the version and CHANGELOG? That's necessary for publishing the change, and the published version of the README is the one most developers will interact with.

You'll also need to merge in the latest master to get the fix for the Linux CI failure.

[stuartmorgan]

I've added a version bump; LGTM.