nicla-system: Add documentation about charging rate.

Author: sebromero

libraries/Nicla_System/src/Nicla_System.h

@@ -77,6 +77,9 @@ class nicla {
    * @brief Enables fast charging of the battery. 
    * 
    * @param mA The desired milliampere (mA) charging current. Range: 5mA - 35mA and 40mA - 300mA. The default is 20mA.
+   * A safe default charging current value that works for most common LiPo batteries is 0.5C, which means charging at a rate equal to half of the battery's capacity.
+   * For example, a 200mAh battery could be charged at 100mA (0.1A).
+   * This charging rate is generally safe for most LiPo batteries and provides a good balance between charging speed and battery longevity.
    * @param disableNtc Whether to disable Temperature Sense and interrupt on charge. The default is true.
    * @return true If the fast charging is enabled successfully. False, otherwise.   
    */