Add IssueHunt sponsor (piotrwitek#92)

Author: kazup01

README.md

@@ -31,6 +31,9 @@ You should check out Playground Project located in the `/playground` folder. It
 ### Contribution Guide
 [CONTRIBUTION.md](/CONTRIBUTION.md)
 
+### Sponsor
+[![issuehunt-image](https://github.com/BoostIO/issuehunt-materials/blob/master/[email protected]?raw=true)](https://issuehunt.io/repos/76996763)
+
 ---
 
 ## Table of Contents