Add pin mapping for SD and SD_MMC examples

libraries/SD/examples/SD_Test/SD_Test.ino

+/*
+ * Connect the SD card to the following pins:
+ *
+ * SD Card | ESP32
+ *    D2       -
+ *    D3       SS
+ *    CMD      MOSI
+ *    VSS      GND
+ *    VDD      3.3V
+ *    CLK      SCK
+ *    VSS      GND
+ *    D0       MISO
+ *    D1       -
+ */
 #include "FS.h"
 #include "SD.h"
 #include "SPI.h"

libraries/SD_MMC/examples/SDMMC_Test/SDMMC_Test.ino

+/*
+ * Connect the SD card to the following pins:
+ *
+ * SD Card | ESP32
+ *    D2       12
+ *    D3       13
+ *    CMD      15
+ *    VSS      GND
+ *    VDD      3.3V
+ *    CLK      14
+ *    VSS      GND
+ *    D0       2  (add 1K pull up after flashing)
+ *    D1       4
+ */
+
 #include "FS.h"
 #include "SD_MMC.h"