Enhance E3 mini V3 config

[clee]

• Link to the Klipper thermistor page instead of hardcoding a list that might be outdated as comments
• Comment out sensor_type lines to force people to pick
• Add FAN2 config

[FHeilmann]

While you're fixing up this config w.r.t. thermistors, could you please move the thermistor definition of Trianglelab NTC100K B3950 above the [extruder] block? If users choose this thermistor with the config as is, the thermistor will be referenced before it is defined, causing errors.

Relevant section of the klipper docs:

Custom thermistors (one may define any number of sections with a "thermistor" prefix). 
A custom thermistor may be used in the sensor_type field of a heater config section.
(For example, if one defines a "[thermistor my_thermistor]" section then one may 
use a "sensor_type: my_thermistor" when defining a heater.) Be sure to 
place the thermistor section in the config file above its first use in a heater section.

[clee]

While you're fixing up this config w.r.t. thermistors, could you please move the thermistor definition of Trianglelab NTC100K B3950 above the [extruder] block? If users choose this thermistor with the config as is, the thermistor will be referenced before it is defined, causing errors.

Good call.