Add RTK data flow diagram

Add a diagram that shows the data flow from the antenna through the GNSS
(ZED-F9P), through the ESP32 to the various external connections such
as:

* USB Serial (Config ESP32)
* USB Serial (Config UBLOX)
* Radio port
* Data port

Author: LeeLeahy2

Firmware/RTK_Surveyor/RTK_Surveyor.ino

@@ -431,6 +431,78 @@ uint32_t max_idle_count = MAX_IDLE_TIME_COUNT;
 uint64_t uptime;
 uint32_t previousMilliseconds;
 
+//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
+/*
+                     +---------------------------------------+      +----------+
+                     |                 ESP32                 |      |   GNSS   |  Antenna
+  +-------------+    |                                       |      |          |     |
+  | Phone       |    |   .-----------.          .--------.   |27  42|          |     |
+  |        RTCM |--->|-->|           |--------->|        |-->|----->|TXD, MISO |     |
+  |             |    |   | Bluetooth |          | UART 2 |   |      | UART1    |     |
+  | NMEA + RTCM |<---|<--|           |<-------+-|        |<--|<-----|RXD, MOSI |<----'
+  +-------------+    |   '-----------'        | '--------'   |28  42|          |
+                     |                        |              |      |          |
+      .---------+    |                        |              |      |          |
+     / uSD Card |    |                        |              |      |          |
+    /           |    |   .----.               V              |      |          |
+   |   Log File |<---|<--|    |<--------------+              |      |          |47
+   |            |    |   |    |               |              |      |    D_SEL |<---- N/C (1)
+   |  Profile # |<-->|<->| SD |<--> Profile   |              |      | 0 = SPI  |
+   |            |    |   |    |               |              |      | 1 = I2C  |
+   |  Settings  |<-->|<->|    |<--> Settings  |              |      |    UART1 |
+   |            |    |   '----'               |              |      |          |
+   +------------+    |                        |              |      |          |
+                     |   .--------.           |              |      |          |
+                     |   |        |<----------'              |      |          |
+                     |   |  USB   |                          |      |          |
+       USB UART <--->|<->| Serial |<-- Debug Output          |      |          |
+    (Config ESP32)   |   |        |                          |      |          |
+                     |   |        |<-- Serial Config         |      |   UART 2 |<--> Radio
+                     |   '--------'                          |      |          |   Connector
+                     |                                       |      |          |  (Correction
+                     |   .------.                            |      |          |      Data)
+        Browser <--->|<->|      |<---> WiFi Config           |      |          |
+                     |   |      |                            |      |          |
+  +--------------+   |   |      |                            |      |      USB |<--> USB UART
+  |              |<--|<--| WiFi |<---- NMEA + RTCM <-.       |      |          |  (Config UBLOX)
+  | NTRIP Caster |   |   |      |                    |       |      |          |
+  |              |-->|-->|      |-----------.        |       |6   46|          |
+  +--------------+   |   |      |           |        |  .----|<-----|TXREADY   |
+                     |   '------'           |        |  v    |      |          |
+                     |                      |      .-----.   |      |          |
+                     |                      '----->|     |   |33  44|          |
+                     |                             |     |<->|<---->|SDA, CS_N |
+                     |           Commands -------->| I2C |   |      |    I2C   |
+                     |                             |     |-->|----->|SCL, CLK  |
+                     |             Status <--------|     |   |36  45|          |
+                     |                             '-----'   |      +----------+
+                     |                                       |
+                     +---------------------------------------+
+                                  26|   |24   A B
+                                    |   |     0 0 = X0, Y0
+                                    V   V     0 1 = X1, Y1
+                                  +-------+   1 0 = X2, Y2
+                                  | B   A |   1 1 = X3, Y3
+                                  |       |
+                                  |     X0|<--- GNSS UART1 TXD
+                                  |       |
+                                  |     X1|<--- GNSS PPS STAT
+                            3 <---|X      |
+                                  |     X2|<--- SCL
+                                  |       |
+                                  |     X3|<--- DAC2
+                   Data Port      |       |
+                                  |     Y0|----> ZED UART1 RXD
+                                  |       |
+                                  |     Y1|<--> ZED EXT INT
+                            2 <-->|Y      |
+                                  |     Y2|---> SDA
+                                  |       |
+                                  |     Y3|---> ADC39
+                                  |       |
+                                  |  MUX  |
+                                  +-------+
+*/
 //-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 
 void setup()