Add SentinelLinearSearch.java and Update README.md

[Krounosity]

Explaination:

Sentinel linear search is an addition to the usual linear search algorithm. Here, the issue of not finding the key (to find) element is removed. We store the last element of the array in a separate variable and put the key in its place.

While the finding index (i) iterates through the array, there are two possible conditions:

• The key element is found before the last index and the loop is broken, or
• The index "i" hits the end of the array

After the interations are completed, the stored last element is put back in its place.

If either the index of the iterative variable (i.e., the value of "I") is smaller than the length of the array-1 or the last element's value (the original value that we put back in place) is equal to the key value, the element is considered to be found and the index is returned

Else, the element is considered to be not found in the array and the index -1 is returned.

The README.md has been updated accordingly

[Krounosity]

Time Complexity: O(n)
Space Complexity: O(1)

[kelvins]

Could you please fix the README links?

[Krounosity]

The changes have been made. Please do check.