Fixing typo

Updating README.md

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Adding Number_16.ipynb

changing font size

Adding Number_15.md link into README.md

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Adding Number_15.md

Adding "PCA using scikit-learn"

Adding "Principal Component Analysis In Scikit-Learn" markdown section

Adding "Calculating Principal Component Analysis"

Adding "Calculating Principal Component Analysis" markdown section

Adding "What Is Principal Component Analysis?" markdown section

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