README: Mention SBUB and free samples

README.md

@@ -18,6 +18,13 @@ Debubo can send messages using any arbitrary Ordered Set, and receive all Ordere
 
 It also gives you control over Rd / Rp resistors on both CC pins, allowing it to act as a Debug Accessory or to simulate plug orientation reversal.
 
+## SBU
+
+Debubo is meant to be used with devices that expose 3.3V UART on their USB-C receptacle's SBU pins.
+
+You can still use Debubo with other devices if you pair it with [SBUB](https://gitlab.com/dos1/sbub). This way you can access other kinds of interfaces exposed on SBU pins as well,
+such as I2C (as seen, for example, on [MacBooks](https://github.com/AsahiLinux/docs/wiki/HW:USB-PD)).
+
 ## Limitations
 
 - there's no control over VBus or a way to sense its state, so make sure both sides always agree on the negotiated voltage!
@@ -66,6 +73,8 @@ and you can find alternative LCSC part numbers in component properties.  You can
 
 When ordering PCBs from JLCPCB, set "Impedance Control" to "Yes", "Layer Stackup" to "JLC04161H-3313" and "Remove Order Number" to "Specify a location".
 
+Free samples of STM32G071CBT6 can be ordered in [ST Online Store](https://estore.st.com/en/stm32g071cbt6-cpn.html).
+
 ## Licensing
 
 © Copyright 2024 [Sebastian Krzyszkowiak](https://dosowisko.net/) <dos@dosowisko.net>