Added nested ternary expression

[mhetreayush]

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Added nested ternary expression with a note:

• Nested Ternary expression:

  let variable = condition ? <return this if true> : 
                <return this if 1st condition is false but this condition is true> :
                <return this if first two conditions are false>
  

• Better to use if..else statements if there are 3 or more conditions.

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