schmatic.md: Add note for UART_TX and UART_RX direction (#402)

Co-authored-by: Jonas Köppeler <[email protected]>

Author: jkoeppeler

hardware/schematic.md

@@ -47,8 +47,8 @@ Below is the pinmap and allocation of the nRF52833, more information is availabl
 | P0.03            | RING1               | N                        | P1                  |
 | P0.04            | RING2               | N                        | P2                  |
 | P0.05            | MIC_IN              | N                        |                     |
-| P0.06            | UART_INT_RX         | PTA18 / P0.03            |                     |
-| P1.08            | UART_INT_TX         | PTA19 / P0.02            |                     |
+| P0.06            | UART_INT_RX`*`     | PTA18 / P0.03            |                     |
+| P1.08            | UART_INT_TX`*`     | PTA19 / P0.02            |                     |
 | P0.08            | I2C_INT_SCL         | PTC1 / P0.29             |                     |
 | P0.10            | GPIO1               | N                        | P8                  |
 | P0.09            | GPIO2               | N                        | P9                  |
@@ -75,6 +75,8 @@ Below is the pinmap and allocation of the nRF52833, more information is availabl
 | P0.31            | COL3                | N                        | P3                  |
 | P0.30            | COL5                | N                        | P10                 |
 
+`*`: These names follow the schematic's naming convention, labeled from the interface's perspective, not the target MCU's. So, UART_INT_TX corresponds to the MCU's RX pin, and UART_INT_RX to the MCU's TX pin.
+
 ## Key Features
 
 Below, we've extracted some useful details about the hardware that anyone implementing software for the micro:bit, interfacing to it, or designing an add-on board for it should find useful.