XS: documentation

doc/features.md

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+# Features (not) available on specific Ledger devices
+
+Nano S has a very limited space for storing applications. It is not enough to fit all Cardano features there, so some of them are only available on Nano S+ and other more spacious Ledger devices (e.g. Nano X and Stax).
+
+The features not supported on Nano S, Cardano app version 7 and above:
+* token minting/burning (but tokens can be included in transaction outputs)
+* pool registration and retirement
+* signing of operational certificates
+* computation of native script hashes
+* details in Byron change outputs (only the address is shown)
+
+Details can be found in [Makefile](../Makefile) and in the code (search for compilation flags beginning with `APP_FEATURE_`).