Clarify what these benchmarks are for (#370)

* Clarify what these benchmarks are for

Signed-off-by: Matteo Collina <hello@matteocollina.com>

* Update README.md

Co-authored-by: Arthur Fiorette <47537704+arthurfiorette@users.noreply.github.com>
Signed-off-by: Matteo Collina <matteo.collina@gmail.com>

---------

Signed-off-by: Matteo Collina <hello@matteocollina.com>
Signed-off-by: Matteo Collina <matteo.collina@gmail.com>
Co-authored-by: Arthur Fiorette <47537704+arthurfiorette@users.noreply.github.com>

README.md

@@ -38,7 +38,8 @@ Disclosure](https://img.shields.io/badge/Security-Responsible%20Disclosure-yello
 # TL;DR
 
 * [Fastify](https://github.com/fastify/fastify) is a fast and low overhead web framework for Node.js.
-* This package shows how fast it is comparatively.
+* This package shows how fast it is compared to other JS frameworks: these benchmarks do not pretend to represent a real-world scenario, but they give a **good indication of the framework overhead**.
+* The benchmarks are run automatically on GitHub actions, which means they run on virtual hardwardware that can suffer from the "noisy neighbor" effect; this means that the results can vary.
 * For metrics (cold-start) see [metrics.md](./METRICS.md)
 
 # Requirements