Use code from README.md in test_readme_sample (backport #144)

[mergify]

This is an automatic backport of pull request #144 done by Mergify.

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[coveralls]

Pull Request Test Coverage Report for Build 1824146160

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.5%) to 82.735%

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Files with Coverage Reduction	New Missed Lines	%
qiskit_finance/data_providers/exchange_data_provider.py	2	73.02%
qiskit_finance/data_providers/wikipedia_data_provider.py	4	73.08%

Totals
Change from base Build 1820499413:	0.5%
Covered Lines:	714
Relevant Lines:	863

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💛 - Coveralls