Added reference

README.md

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+
+                        
+                                                                 +-----------------------+
+                                                                 | O      | USB |      O |
+                                                                 |        -------        |
+                                                             3V3 | [ ]               [ ] | VIN                                  [ 5V FROM RPi      ]                    
+     [ Ground From Pi  ]                                     GND | [ ]               [ ] | GND                                  [ GROUND FROM RPi  ]
+     [                 ]     Touch3 / HSPI_CS0 / ADC2_3 / GPIO15 | [ ]               [ ] | GPIO13 / ADC2_4 / HSPI_ID / Touch4   [ BUTTON_MENU      ]
+     [                 ] CS / Touch2 / HSPI_WP / ADC2_2 /  GPIO2 | [ ]               [ ] | GPIO12 / ADC2_5 / HSPI_Q / Touch5    [ BUTTON_BACK      ]
+     [                 ]      Touch0 / HSPI_HD / ADC2_0 /  GPIO4 | [ ]               [ ] | GPIO14 / ADC2_6 / HSPI_CLK / Touch6  [ BUTTON_UP        ]
+     [                 ]                         U2_RXD / GPIO16 | [ ]               [ ] | GPIO27 / ADC2_7 / Touch7             [ BUTTON_DOWN      ] 
+     [                 ]                         U2_TXD / GPIO17 | [ ]               [ ] | GPIO26 / ADC2_9 / DAC2               [                  ]
+     [                 ]                      V_SPI_CS0 /  GPIO5 | [ ]  ___________  [ ] | GPIO25 / ADC2_8 / DAC1               [                  ]
+     [                 ]                SCK / V_SPI_CLK / GPIO18 | [ ] |           | [ ] | GPIO33 / ADC1_5 / Touch8 / XTAL32    [                  ]
+     [                 ]        U0_CTS / MSIO / V_SPI_Q / GPIO19 | [ ] |           | [ ] | GPIO32 / ADC1_4 / Touch9 / XTAL32    [                  ]
+     [ SDA to Pi       ]                 SDA / V_SPI_HD / GPIO21 | [ ] |           | [ ] | GPIO35 / ADC1_7                      [                  ] 
+     [                 ]                  CLK2 / U0_RXD /  GPIO3 | [ ] |           | [ ] | GPIO34 / ADC1_6                      [                  ]
+     [                 ]                  CLK3 / U0_TXD /  GPIO1 | [ ] |           | [ ] | GPIO39 / ADC1_3 / SensVN             [                  ]
+     [ SCL to Pi       ]        SCL / U0_RTS / V_SPI_WP / GPIO22 | [ ] |           | [ ] | GPIO36 / ADC1_0 / SensVP             [                  ] 
+     [                 ]                MOSI / V_SPI_WP / GPIO23 | [ ] |___________| [ ] | EN 
+                                                                 |                       |
+                                                                 |  |  |  ____  ____  |  |
+                                                                 |  |  |  |  |  |  |  |  |
+                                                                 |  |__|__|  |__|  |__|  |
+                                                                 | O                   O |
+                                                                 +-----------------------+
+                             
+Power Pins
+----------
+
+VIN - VIN pin can be used to directly supply the ESP32 and its peripherals, if you have a regulated 5V voltage source.
+3V3 - 3.3V pin is the output of an on-board voltage regulator. This pin can be used to supply power to external components.
+GND - Ground pin(s)
+
+GPIO Pins
+---------
+ESP32 development board has 25 GPIO pins which can be assigned to various functions programmatically. 
+Each digital enabled GPIO can be configured to internal pull-up or pull-down, or set to high impedance. 
+When configured as an input, it can also be set to edge-trigger or level-trigger to generate CPU interrupts.
+ 
+ADC Channels
+------------
+The board integrates 12-bit SAR ADCs and supports measurements on 15 channels (analog enabled pins). 
+Some of these pins can be used to build a programmable gain amplifier which is used for the measurement of 
+small analog signals. The ESP32 is also designed to measure the voltages while operating in the sleep mode.
+
+DAC Channels
+------------
+he board features two 8-bit DAC channels to convert digital signals into true analog voltages. This dual DAC
+can drive other circuits.
+
+Touch Pads
+----------
+The board offers 9 capacitive sensing GPIOs which detect capacitive variations introduced by the GPIO’s direct
+contact or close proximity with a finger or other objects.
+
+UART Pins
+---------
+ESP32 development board has 2 UART interfaces, i.e. UART0 and UART2, which provide asynchronous communication 
+(RS232 and RS485) and IrDA support, and communicate at up to 5 Mbps. UART provides hardware management of the 
+CTS and RTS signals and software flow control (XON and XOFF) as well.
+ 
+SPI Pins
+--------
+SPI Pins ESP32 features three SPIs (SPI, HSPI and VSPI) in slave and master modes. These SPIs also support the 
+following general-purpose SPI features:
+
+  - 4 timing modes of the SPI format transfer
+  - Up to 80 MHz and the divided clocks of 80 MHz
+  - Up to 64-Byte FIFO
+  - All SPIs can also be used to connect to the external Flash/SRAM and LCD.
+
+PWM Pins
+--------
+The board has 25 channels (Nearly All GPIO pins) of PWM pins controlled by Pulse Width Modulation (PWM) controller.
+The PWM output can be used for driving digital motors and LEDs. The controller consists of PWM timers and the PWM 
+operator. Each timer provides timing in synchronous or independent form, and each PWM operator generates the waveform
+for one PWM channel.
+
+
+EN Pin
+------
+Used to enable ESP32. The chip is enabled when pulled HIGH. When pulled LOW the chip works at minimum power.