Arduino pins vs Esp8266MOD
table filled

 * Typical pin layout used:
 * ------------------------------------------------------
 *             MFRC522      Arduino       NodeMCU
 *             Reader/PCD   Uno/101       ESP8266MOD
 * Signal      Pin          Pin           Pin       
 * ------------------------------------------------------
 * RST/Reset   RST          9             any, recommended 5
 * SPI SS      SDA(SS)      10            any, recommended 4, possible 15
 * SPI MOSI    MOSI         11 / ICSP-4   13
 * SPI MISO    MISO         12 / ICSP-1   12
 * SPI SCK     SCK          13 / ICSP-3   14


io 15 is SS if esp8266 is slave. but this pin must be LOW at boot. you can use it as SS if SS pin of reader doesn't pull-up.

io 4 and io 5 are untroubled pins.

io 0 and io 2 are with io 15 boot configuration pins and can be used only if they don't change the required boot state.

io 1 and io 3 are Serial interface

io 16 is RTC pin and is used for wake up from deep slepp

warning: does the reader work with 3.3 V?