docs/readme: Day of the Year

Author: mmkvdev

Problems/DayOfTheYear/README.md

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+### 1154. Day of the Year
+
+
+### Problem Statement
+Given a string date representing a Gregorian calendar date formatted as YYYY-MM-DD, return the day number of the year.
+
+ 
+
+### Example 1:
+```
+Input: date = "2019-01-09"
+Output: 9
+```
+
+**Explanation**: ``` Given date is the 9th day of the year in 2019.```
+
+### Example 2:
+```
+Input: date = "2019-02-10"
+Output: 41
+```
+
+### Example 3:
+```
+Input: date = "2003-03-01"
+Output: 60
+```
+
+### Example 4:
+```
+Input: date = "2004-03-01"
+Output: 61
+```
+
+### Constraints:
+
+* date.length == 10
+* date[4] == date[7] == '-', and all other date[i]'s are digits
+* date represents a calendar date between Jan 1st, 1900 and Dec 31, 2019.