Multicopter PID Tuning Cookbook: Add overall structure & Thrust Curve

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Rename pid_multicopter to pid_multicopter_cookbook for easier Review

- Previous file was interfering the view in the diff of the PR, this
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en/config_mc/pid_tuning_guide_multicopter_cookbook.md

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+# Multicopter PID Tuning Cookbook
+
+This document will guide you through the whole PID tuning process of Multicopter step by step, just like a cookbook!
+
+## Step 1: Hardware configuration
+
+### Check motor output settings
+First things first, you need to make sure your motors are configured correctly!
+
+If you are using PWM output, set the correct Disarmed, Minimum and Maximum output value by referring to [Actautor Outputs > Motor Configuration](../config/actuators.md#motor-configuration).
+
+It is important to set PWM minimum value properly to make sure motors won't stop spinning in the air.
+
+### Setting motor thrust curve factor
+
+<!-- TODO: Insert Thrust curve simulation (interactive diagram) -->
+
+Thrust curve factor([THR_MDL_FAC](../advanced_config/parameter_reference.md#THR_MDL_FAC)) defines the relationship between output signal and the thrust generated by the motor.
+
+This is important to set correctly, as the most fundamental rate control of the PID controller will output a torque setpoint which will get mapped to appropriate signal value depending on the thrust curve factor.
+
+Therefore, if you set it to be `linear` (`thrust = signal`) when in reality it is `quadratic`(`thrust = signal^2`), the vehicle dynamics assumption will be wrong and it may behave erratically.
+
+<!-- TODO: Insert diagram showing Thrust Curve's effect on control authority -->
+
+This is highly dependent on the ESC, Motor and Propeller (and even Battery), so it should be evaluated for every specific setup.
+
+Refer to [Thrust Curve](pid_tuning_guide_multicopter_advanced.md#thrust-curve) documentation for the detailed explanation of a Thrust Curve.
+
+The best case is to have an actual thrust measurement data that you can plot and fit onto the thrust curve. Depending on that please jump to appropriate sections below:
+
+- [If you have a thrust measurement, jump to here](#if-you-have-a-thrust-measurement-data)
+- [If you don't have a thrust measurement, jump to here](#if-you-dont-have-a-thrust-measurement-data)
+
+#### If you have a thrust measurement data
+
+If you have the thrust measurement for your ESC, motor and propeller combination, simply plot the data in a tool (e.g. Excel) and find for the best `alpha` value that fits the thrust curve data, and set it as the thrust curve factor parameter.
+
+*rel_thrust = ( `alpha` ) * rel_signal^2 + ( 1 - `alpha` ) * rel_signal*
+
+An example of a thrust measurement is something like this: [EXAMPLE](https://github.com/Auterion/thrust-bench-data/blob/master/StepsTest_2019-04-30_112217_MT2212-11_1100kv_APC10x5-5_low.csv).
+
+And this example plots to a thrust curve like below, and the appropriate thrust curve factor is identified as 0.X. (TODO)
+
+#### If you don't have a thrust measurement data
+
+This is most likely the case since most people don't have a thrust measurement system available, in that case we can select empirically depending on the type of ESC:
+
+- Set to `1.0` if your ESC explicitly states that it does RPM control (RPM proportional to signal), since thrust will be fully quadratic (proportional to `signal^2`).
+- Set to `0.3` for all other ESCs. Which is an empirically derived value that assimilates *most* ESC / Motor / Propeller combination).
+
+If you don't set any value, the default will be `0.0`, which assumes linear relationship between signal and the thrust.
+
+## Step 2: Pre conditions
+
+## Step 3: Rate control tuning
+
+## Step 4: Attitude control tuning
+
+## Step 5: Velocity control tuning
+
+## Step 6: Position control tuning
+
+## Step 7: Gyro filter tuning
+