add hello world benchmark type

Author: programatik29

README.md

@@ -2,5 +2,11 @@
 
 Benchmarking web frameworks written in [rust] with [rewrk] tool.
 
+## Benchmark Types
+
+### Hello World
+
+Respond "Hello, world!" to every request on "/" endpoint.
+
 [rewrk]: https://github.com/ChillFish8/rewrk
 [rust]: https://github.com/rust-lang/rust