docs(php): add information about supported php versions

Author: Xenira

README.md

@@ -116,6 +116,10 @@ best resource at the moment. This can be viewed at [docs.rs].
 - Linux, macOS or Windows-based operating system.
 - PHP 8.0 or later.
   - No support is planned for earlier versions of PHP.
+  - PHP versions, that no longer receive security updates, will be dropped.
+  - PHP 8.0 is now **deprecated** and will be dropped in the future.
+  - See https://www.php.net/supported-versions.php for information on PHP
+    supported versions and their end of life dates.
 - Rust.
   - Currently, we maintain no guarantee of a MSRV, however lib.rs suggests Rust
     1.57 at the time of writing.