doc: add conan badge to README (#1096)

README.md

@@ -7,6 +7,7 @@
 [![Coverage](https://codecov.io/gh/skypjack/entt/branch/master/graph/badge.svg)](https://codecov.io/gh/skypjack/entt)
 [![Try online](https://img.shields.io/badge/try-online-brightgreen)](https://godbolt.org/z/zxW73f)
 [![Vcpkg port](https://img.shields.io/vcpkg/v/entt)](https://vcpkg.link/ports/entt)
+[![Conan Center](https://img.shields.io/conan/v/entt)](https://conan.io/center/recipes/entt)
 [![Documentation](https://img.shields.io/badge/docs-doxygen-blue)](https://skypjack.github.io/entt/)
 [![Gitter chat](https://badges.gitter.im/skypjack/entt.png)](https://gitter.im/skypjack/entt)
 [![Discord channel](https://img.shields.io/discord/707607951396962417?logo=discord)](https://discord.gg/5BjPWBd)