Document unsupported outdated functions

We do not support old firmware versions on the Nitrokey Storage, so we
document that these outdated functions are not supported:
- NK_set_unencrypted_volume_rorw_pin_type_user
- NK_set_unencrypted_read_only
- NK_set_unencrypted_read_write
- NK_set_encrypted_read_only
- NK_set_encrypted_read_write

1 files changed, 10 insertions, 4 deletions

diff --git a/README.md b/README.md
index c0799a9..567ae58 100644
--- a/README.md
+++ b/README.md
@@ -21,15 +21,21 @@ available but still under development.
 The following functions provided by `libnitrokey` are deliberately not
 supported by `nitrokey-rs`:
 
-- `NK_get_device_model()`.  We know which model we connected to, so we can
+- `NK_get_device_model`.  We know which model we connected to, so we can
   provide this information without calling `libnitrokey`.
-- `NK_get_time()`.  This method is useless as it will always cause a timestamp
+- `NK_get_time`.  This method is useless as it will always cause a timestamp
   error on the device (see [pull request #114][] for `libnitrokey` for details).
-- `NK_get_status()`.  This method only provides a string representation of
+- `NK_get_status`.  This method only provides a string representation of
   data that can be accessed by other methods (firmware version, serial number,
   configuration).
-- `NK_get_status_storage_as_string()`.  This method only provides an incomplete
+- `NK_get_status_storage_as_string`.  This method only provides an incomplete
   string representation of the data returned by `NK_get_status_storage`.
+- `NK_set_unencrypted_volume_rorw_pin_type_user`,
+  `NK_set_unencrypted_read_only`, `NK_set_unencrypted_read_write`,
+  `NK_set_encrypted_read_only` and `NK_set_encrypted_read_write`.  These
+  methods are only relevant for older firmware versions (pre-v0.51).  As the
+  Nitrokey Storage firmware can be updated easily, we do not support these
+  outdated versions.
 
 ## Tests