message: add WM_RTC def for rtc.h
diff: #ifndef WiFiManager_h
  #define WiFiManager_h
  -#define WM_WEBSERVERSHIM // use webserver shim lib
  -// #define WM_MDNS // use MDNS
  +// #define WM_MDNS // also set MDNS with sethostname
  // #define WM_FIXERASECONFIG // use erase flash fix
  -// #define WM_ERASE_NVS // esp32 erase() will erase
  +// #define WM_ERASE_NVS // esp32 erase(true) will erase NVS
  +// #define WM_RTC // esp32 info page will include reset reasons
  +
  +#define WM_WEBSERVERSHIM // use webserver shim lib
  #ifdef ESP8266
  #ifdef WM_MDNS
  #include <ESPmDNS.h>
  #endif
  +
  + #ifdef WM_RTC
  + #include <rom/rtc.h>
  + #endif
  +
  +
  #else
  #endif
  