Add hint for RISC-V users to check serial console for full trace

Co-Authored-By: J. Nick Koston <nick@koston.org>

esphome/components/esp32/crash_handler.cpp

@@ -114,6 +114,9 @@ void crash_handler_log() {
     pos += snprintf(hint + pos, sizeof(hint) - pos, " 0x%08" PRIX32, addr);
   }
   ESP_LOGE(TAG, "%s", hint);
+#if CONFIG_IDF_TARGET_ARCH_RISCV
+  ESP_LOGE(TAG, "RISC-V backtrace is best-effort. Check serial console for full register dump.");
+#endif
 }
 
 }  // namespace esphome::esp32