Create interpolationSearch.c

[Abhishek-Greninja17]

added all possible test cases including condition check for better understanding
provided all essentials to know about the implementation in form of comments
code is providing expected outcome for each test cases

codition check can be ommited if not necessary

This PR implements the code for interpolationSearch in C referred in issue #211

I have read the contributing guidelines in CONTRIBUTING.md and have ensured the following:

• My code is placed in the required directory as outlined in CONTRIBUTING.md
• My code file is named according to CONTRIBUTING.md
• Variables, classes, functions etc. follow camel case as outlined in CONTRIBUTING.md
• My code hasn't been implemented or claimed by someone else and I have checked the present issues and PRs for the same
• My code is well commented
• If my code is the first implementation of interpolationSearch, I have added the link to this directory in README.md
• I have not copied my code from anywhere

This PR creates/modifies the README for

I have read the contributing guidelines in CONTRIBUTING.md and have ensured the following:

• Algo name (as heading)
• A small description about algo
• Time Complexity (Worst, Average, Best case)
• Space Complexity (Worst, Average, Best case)
• Logic and Pseudocode
• Instructions for running code

[deutranium]

Wow, this is a truly amazing code!
Thank you for contributing!

[Abhishek-Greninja17]

Thank you
Glad to contribute!