add some documentation links to the em7180.c header

Drivers/EM7180/Src/em7180.c

@@ -22,6 +22,8 @@
 /*
  * EM7180 SENtral register map
  * see http://www.emdeveloper.com/downloads/7180/EMSentral_EM7180_Register_Map_v1_3.pdf
+ * see also https://github.com/kriswiner/EM7180_SENtral_sensor_hub/wiki/D.-The-Host-Side-Program
+ * see also https://www.weizmann.ac.il/sci-tea/benari/sites/sci-tea.benari/files/uploads/softwareAndLearningMaterials/quaternion-tutorial-2-0-1.pdf
  */
 #define EM7180_QX                 0x00 /* this is a 32-bit normalized floating point number read from registers 0x00-03 */
 #define EM7180_QY                 0x04 /* this is a 32-bit normalized floating point number read from registers 0x04-07 */