docs: add short PRF guide

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

docs/development/prf.md

@@ -0,0 +1,40 @@
+# PRF
+
+PRF (Pebble Recovery Firmware) is a special firmware image available for recovery purposes.
+It allows connecting from a phone to, for example, flash a new firmware image even if the main firmware is broken or unavailable.
+
+## Building
+
+Once a project is configured, PRF image can be built by running:
+
+```shell
+./waf build_prf
+```
+
+## Flashing
+
+The PRF image can be flashed directly into the application area by running:
+
+```shell
+./waf flash_prf
+```
+
+This is useful when developing PRF features because the watch will boot directly to PRF.
+To flash it to the external flash, so it can be used regularly, run:
+
+```shell
+./waf image_recovery
+```
+
+Append `--tty` option if needed.
+In such case, PRF will need to be copied to the main flash to run.
+This can be done by pressing {kbd}`BACK` + {kbd}`UP` + {kbd}`MIDDLE` when
+booting, or holding {kbd}`BACK` for 7-10s while in the main application.
+
+## Console
+
+You can interact with PRF console by running:
+
+```shell
+./waf console_prf
+```

docs/index.md

@@ -4,3 +4,9 @@
 :hidden:
 getting_started.md
 ```
+
+```{toctree}
+:hidden:
+:caption: 🛠️ Development
+development/prf.md
+```