README.md: add some warning about RISCV support

Author: thomas-roos

README.md

@@ -37,6 +37,10 @@ The `main` branch contains ongoing development work and:
 - Could include breaking changes.
 - Is not recommended for production use.
 
+### ⚠️ RISC-V Support Warning
+
+RISC-V architecture support is experimental and not fully tested. Use with caution in production environments.
+
 ## Supported Greengrass V2 IPC commands (Features)
 
 IPC support is provided by ggipcd. The support is translating the IPC command to