T4 Support - fix pin 17 update comments

I updated the comments in readme plus example apps, showing pin numbers.

I also fixed pin 17.  So far I have only tried 1, 8, 14, 16, 20 as simply using breadboard version

WS2812Serial.cpp

 	  case 17: // Serial4
 		uart = &IMXRT_LPUART3; 
 		CCM_CCGR0 |= CCM_CCGR0_LPUART3(CCM_CCGR_ON);
-		hwtrigger = DMAMUX_SOURCE_LPUART4_TX; 
+		hwtrigger = DMAMUX_SOURCE_LPUART3_TX; 
 		break;
 	  case 20: // Serial5
 	  case 39: // Serial5 alt

examples/BasicTest/BasicTest.ino

 //   Teensy 3.2:  1, 5, 8, 10, 31   (overclock to 120 MHz for pin 8)
 //   Teensy 3.5:  1, 5, 8, 10, 26, 32, 33, 48
 //   Teensy 3.6:  1, 5, 8, 10, 26, 32, 33
+//   Teensy 4.0:  1, 8, 14, 16, 20, 24, 29, 39
 
 byte drawingMemory[numled*3];         //  3 bytes per LED
 DMAMEM byte displayMemory[numled*12]; // 12 bytes per LED

examples/FastLED_Cylon/FastLED_Cylon.ino

 //   Teensy 3.2:  1, 5, 8, 10, 31   (overclock to 120 MHz for pin 8)
 //   Teensy 3.5:  1, 5, 8, 10, 26, 32, 33, 48
 //   Teensy 3.6:  1, 5, 8, 10, 26, 32, 33
+//   Teensy 4.0:  1, 8, 14, 16, 20, 24, 29, 39
 #define DATA_PIN 1
 
 // Define the array of leds

readme.md

 
 ## Supported Pins & Serial Ports
 
-| Port    | Teensy LC   | Teensy 3.2 | Teensy 3.5 | Teensy 3.6 |
-| :------ | :---------: | :--------: | :--------: | :--------: |
-| Serial1 | 1, 4, 5, 24 | 1, 5       | 1, 5, 26   | 1, 5, 26   |
-| Serial2 |             | 10, 31     | 10         | 10         |
-| Serial3 |             | 8          | 8          | 8          |
-| Serial4 |             |            | 32         | 32         |
-| Serial5 |             |            | 33         | 33         |
-| Serial6 |             |            | 48         |            |
+| Port    | Teensy LC   | Teensy 3.2 | Teensy 3.5 | Teensy 3.6 | Teensy 4.0 |
+| :------ | :---------: | :--------: | :--------: | :--------: | :--------: |
+| Serial1 | 1, 4, 5, 24 | 1, 5       | 1, 5, 26   | 1, 5, 26   | 1          |
+| Serial2 |             | 10, 31     | 10         | 10         | 8          |
+| Serial3 |             | 8          | 8          | 8          | 14         |
+| Serial4 |             |            | 32         | 32         | 17         |
+| Serial5 |             |            | 33         | 33         | 20,39?     |
+| Serial6 |             |            | 48         |            | 29         |
 
 Serial2 & Serial3 on Teensy LC are not supported, due to lack of configurable
 oversampling needed to run at the high speed required.