Change instructions since elf-to-uf2 is missing

doc/exploring-cheriot-rtos.md

@@ -39,11 +39,12 @@ xmake -P cheriot-rtos/examples/05.sealing/
 ### Where's my UF2?
 
 If you've followed the '[running software on the FPGA]' guide, you'll expect UF2 files as part of the build artefacts but these aren't automatically created in the [`cheriot-rtos`][] repository.
-Thankfully, this repository includes a `./scripts/elf-to-uf2.sh` script that converts an ELF into a firmware a UF2 file.
-
-[running software on the FPGA]: ./guide/running-software.md#running-on-the-sonata-fpga
+You can generate it using the following commands:
 
 ```sh
 xmake -P cheriot-rtos/examples/05.sealing/
-./scripts/elf-to-uf2.sh build/cheriot/cheriot/release/sealing
+llvm-strip build/cheriot/cheriot/release/sealing -o sealing_stripped.elf
+uf2conv -b 0x0000 -f 0x6ce29e60 sealing_stripped.elf -co sealing.elf.uf2
 ```
+
+[running software on the FPGA]: ./guide/running-software.md#running-on-the-sonata-fpga