Update README

README.md

@@ -8,7 +8,7 @@ It's extremely easy to set up. Just include the **[httplib.h](https://raw.github
 Learn more in the [official documentation](https://yhirose.github.io/cpp-httplib/) (built with [docs-gen](https://github.com/yhirose/docs-gen)).
 
 > [!IMPORTANT]
-> This library uses 'blocking' socket I/O. If you are looking for a library with 'non-blocking' socket I/O, this is not the one that you want.
+> This library uses 'blocking' socket I/O. If you are looking for a library with 'non-blocking' socket I/O, this is not the one that you want. Only **HTTP/1.1** is supported — HTTP/2 and HTTP/3 are not implemented.
 
 > [!WARNING]
 > 32-bit platforms are **NOT supported**. Use at your own risk. The library may compile on 32-bit targets, but no security review has been conducted for 32-bit environments. Integer truncation and other 32-bit-specific issues may exist. **Security reports that only affect 32-bit platforms will be closed without action.** The maintainer does not have access to 32-bit environments for testing or fixing issues. CI includes basic compile checks only, not functional or security testing.