Add link to PHP module (#361)

Co-authored-by: Caleb Maclennan <caleb@alerque.com>
Co-authored-by: Eemeli Aro <eemeli@mozilla.com>

README.md

@@ -53,6 +53,7 @@ We also know about the following community-driven implementations:
   - A Lua implementation effort is underway at [`fluent-lua`](https://github.com/alerque/fluent-lua) by [@alerque](https://github.com/alerque).
   - A D implementation effort is underway at [`fluentd`](https://github.com/SirNickolas/fluentd) by [@SirNickolas](https://github.com/SirNickolas).
   - [`fluent.go`](https://github.com/lus/fluent.go) - a Golang implementation by [@lus](https://github.com/lus)
+  - [`fluent-php`](https://github.com/Ennexa/fluent-php) - a PHP module providing bindings wrapping the Rust library by [@Ennexa](https://github.com/Ennexa)
 
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