Add solution for First Missing Positive in Hashing

[Ace117MC]

What's being changed:

I added a solution for First Positive Missing Integer problem available for Hashing category. This questions does not use conventional hash table and instead uses the given list as hash table which provides other possible solutions to solving hash problems.

Checkoff the following:

• [X] Read Contribution.md
• [X] Created a new branch before committing.
• [X] My File doesn't contain any duplicacy or misinformation (isn't available in the library).
• [X] Added to the right category.
• [ ] Added "add code" label.
• [X] Described what's being changed.

[Ace117MC]

Please review and and labels. I am unable to add labels since I do not have access