docs: Embed image directly in Time Complexity Graph section

[Musaddiq625]

Replaced the text link to the complexity graph with a direct image embed. This makes the graph visible without needing to click the link.

Welcome to Dart community

Describe your change:

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Documentation change?
• Add/Update/Fix test cases.

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Dart files are placed inside an existing directory.
• All new algorithms have a URL in its comments that points to Wikipedia or other similar explanation.
• If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[Musaddiq625]

@akashgk @Parowicz please review

[Musaddiq625]

@akashgk @Parowicz
Is this repo active?
I'm hoping to get this merged before October ends, aiming to complete it for Hacktoberfest