document working cards for rc522 (#2374)

components/rfid-reader/RC522/README.md

@@ -1,4 +1,6 @@
-# How to setup the RC522 RFID reader
+# RC522 Reader
+
+## How to setup the RC522 RFID reader
 
 1. **You can use the `setup_rc522.sh` script (recommended)** or follow the manual steps:
 
@@ -15,3 +17,7 @@
    - `sudo systemctl restart phoniebox-rfid-reader.service`
 
 Be aware that unlike a few other installations with this card reader the phoniebox requires the IRQ pin to be connected (on the raspberry pi and zero normaly to GPIO 24 or PIN 18).
+
+## Working cards/tags
+
+Cards or tags must support 13.56 MHz. Currently, only cards/tags of the type "NXP Mifare Classic 1k(S50)", "NXP Mifare Classic 4k(S70)" and "NXP Mifare Ultralight (C)" can be used. Type "NXP Mifare NTAG2xx" will not work!