README: mention the minimum supported Ledger Bitcoin app version

Fixes #203

README.md

@@ -95,7 +95,14 @@ timelock (the only type of timelocks supported for now), time starts ticking whe
 payment. That is if you want the recovery path to never be available, each coin must be spent
 at least once every `N` blocks. (With `N` the configured value of the timelock.)
 
-For now, only the Ledger and Specter DIY signing devices are supported, as Miniscript compatibility of the signer is a must. We expect more signing devices to implement Miniscript capability. We may add the possibility to use Liana as a "hot" wallet in the future (i.e. with a private key directly on the laptop).
+For now, only the Ledger and Specter DIY signing devices are supported, as Miniscript compatibility
+of the signer is a must. We expect more signing devices to implement Miniscript capability. We may
+add the possibility to use Liana as a "hot" wallet in the future (i.e. with a private key directly
+on the laptop).
+
+If you are using a Ledger device, make sure to install the currently latest version of the Bitcoin
+application: `2.1.0`. This is the minimum supported version, as it's the first one to introduce
+support for Miniscript.
 
 If you are using the GUI, it should be intuitive what menu to use depending on your intention. If it
 is not, bug report are very welcome so [feel free to report it](https://github.com/revault/liana/issues)! :)