Update README.md

Author: Jaskaran Singh

README.md

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 | 8 | String to Integer (atoi) | Implement atoi which converts a string to an integer. | [Solution](string_to_integer.js) |
 | 65 | Valid Number | Validate if a given string can be interpreted as a decimal number. | [Solution](valid_number.js) |
 | 665 | Non-decreasing Array | Given an array nums with n integers, your task is to check if it could become non-decreasing by modifying at most 1 element. We define an array is non-decreasing if nums[i] <= nums[i + 1] holds for every i (0-based) such that (0 <= i <= n - 2). | [Solution](non_decreasing_array.js) |
+| 709 | To Lower Case | Implement function ToLowerCase() that has a string parameter str, and returns the same string in lowercase. | [Solution](to_lower_case.js) |
 | 771 | Jewels and Stones | You're given strings J representing the types of stones that are jewels, and S representing the stones you have.  Each character in S is a type of stone you have.  You want to know how many of the stones you have are also jewels. The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A". | [Solution](jewels_and_stones.js) |
 | 1108 | Defanging an IP Address | Given a valid (IPv4) IP address, return a defanged version of that IP address. A defanged IP address replaces every period "." with "[.]". | [Solution](ip_defanging.js) |
 | 1281 | Subtract the Product and Sum of Digits of an Integer | Given an integer number n, return the difference between the product of its digits and the sum of its digits. | [Solution](subtract_product_and_sum_integer.js) |