Add a guard statement for ESP8266
Fixes
#endif // DEBUG_DISABLED
#endif // REMOTE_DEBUG
+#if ESP8266
+#error "ESP8266 isn't supported by SensESP version 2. To compile an existing project, add @^1.0.0 to the SensESP depdenency in platformio.ini."
+#endif
+
namespace sensesp {
// Typically, pulling a namespace into another is something to be avoided,
