Added initial code reference

docs/reference.md

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+# Pimoroni Explorer- Library Reference <!-- omit in toc -->
+
+This is the library reference for the [Pimoroni Explorer](https://shop.pimoroni.com/products/explorer), an electronics adventure playground, powered by the Raspberry Pi RP2350.
+
+
+## Table of Content <!-- omit in toc -->
+- [Getting Started](#getting-started)
+- [Reading the Switches](#reading-the-switches)
+- [`explorer` Reference](#explorer-reference)
+  - [Index Constants](#index-constants)
+  - [Count Constants](#count-constants)
+  - [Colour Constants](#colour-constants)
+  - [Pin Constants](#pin-constants)
+  - [Audio Constants](#audio-constants)
+  - [Variables](#variables)
+  - [Functions](#functions)
+
+
+## Getting Started
+
+To start coding your Pimoroni Explorer, you will need to add the following line to the start of your code file.
+
+```python
+import explorer
+```
+
+...
+
+
+## Reading the Switches
+
+...
+
+
+## `explorer` Reference
+
+### Index Constants
+```python
+SERVO_1 = 0
+SERVO_2 = 1
+SERVO_3 = 2
+SERVO_4 = 3
+```
+
+### Count Constants
+```python
+NUM_GPIOS = 6
+NUM_ADCS = 6
+NUM_SERVOS = 4
+NUM_SWITCHES = 6
+```
+
+### Colour Constants
+```python
+WHITE = 65535
+BLACK = 0
+CYAN = 65287
+MAGENTA = 8184
+YELLOW = 57599
+GREEN = 57351
+RED = 248
+BLUE = 7936
+```
+
+### Pin Constants
+```python
+SWITCH_A_PIN = 16
+SWITCH_B_PIN = 15
+SWITCH_C_PIN = 14
+SWITCH_X_PIN = 17
+SWITCH_Y_PIN = 18
+SWITCH_Z_PIN = 19
+SWITCH_USER_PIN = 22
+
+I2C_SDA_PIN = 20
+I2C_SCL_PIN = 21
+
+SERVO_1_PIN = 9
+SERVO_2_PIN = 8
+SERVO_3_PIN = 7
+SERVO_4_PIN = 6
+
+ADC_0_PIN = 40
+ADC_1_PIN = 41
+ADC_2_PIN = 42
+ADC_3_PIN = 43
+ADC_4_PIN = 44
+ADC_5_PIN = 45
+
+GPIO_0_PIN = 0
+GPIO_1_PIN = 1
+GPIO_2_PIN = 2
+GPIO_3_PIN = 3
+GPIO_4_PIN = 4
+GPIO_5_PIN = 5
+
+PWM_AUDIO_PIN = 12
+AMP_EN_PIN = 13
+```
+
+### Audio Constants
+```python
+AMP_CORRECTION = 4
+DEFAULT_VOLUME = 0.2
+```
+
+### Variables
+```python
+i2c: PimoroniI2C
+audio_pwm: PWM
+
+button_a: Pin
+button_b: Pin
+button_c: Pin
+button_x: Pin
+button_y: Pin
+button_z: Pin
+button_user: Pin
+
+display: PicoGraphics
+
+servos: list[Servo]
+```
+
+### Functions
+```python
+play_tone(frequency: float) -> None
+play_silence() -> None
+stop_playing() -> None
+set_volume(volume: float=None) -> None
+mute_audio(value: bool=True) -> None
+```