Typos / Readme.md

There are a few typos:

1. line №5
> “…In this case, the player (game **objets**)…” should be replaced with
> “…In this case, the player (game **objects**)…”.
2. line №15
> “…entities that have a **Healt**…” should be replaced with
> “…entities that have a **Health**…”
3. line №17
> “…this **sytem** is needed…” should be replaced with
> “…this **system** is needed…”.