https://arduino-esp8266.readthedocs.io/en/latest/ota_updates/readme.html
#ifndef __WIFI_CREDENTIALS_H
#define __WIFI_CREDENTIALS_H
#ifndef STASSID
#define STASSID "ssid"
#define STAPSK "key"
#endif
#endif // __WIFI_CREDENTIALS_H
change IP of esp8266 accordingly IP gets printed on Serial Monitor after first Upload