Add fuse chapter to signing troubleshooting (#1369)

Author: fallberg

core/MySigning.h

@@ -892,5 +892,16 @@ int signerMemcmp(const void* a, const void* b, size_t sz);
  * Also, if whitelisting is used, make sure the proper serial is paired with the proper node ID at the destination.
  * Whitelisting preferences are communicated with the signing presentation (done automatically from nodes to gateway but
  * has to be explicitly done by sketch for node to node communication). @see signerPresentation
+ *
+ * @subsection MySigningTroubleshootingSymptomStTampered Signing backend reports tampered even after personalization
+ *
+ * The signing backend validates that the secure elements in EEPROM remain unmodified after personalization using a checksum. If the check fails,
+ * the backend reports
+ * @code
+ * !SGN:PER:Tampered
+ * @endcode
+ * This usually indicate that the sketch has modified the secure elements in EEPROM, but if you experience this even after a node is freshly
+ * personalized on a atmega device, it could be that the EESAVE fuse bit is not set which mean that the EEPROM is erased when a new firmware is flashed.
+ * You will need to enable the EESAVE bit in order to have the security personalization persist in the node.
  */
 /** @}*/