chore(cli): add docustring to `index_management`

diff --git a/python/docs/OPTIONS.rst b/python/docs/OPTIONS.rst
index d3eb091d..706e2543 100644
--- a/python/docs/OPTIONS.rst
+++ b/python/docs/OPTIONS.rst
@@ -313,7 +313,7 @@ Evolu commands.
   Commands:
     get-delegated-identity-key  Request the delegated identity key of this device.
     get-node                    Return the SLIP-21 node for Evolu.
-    index-management
+    index-management            Read the rotation index for the delegated identity key.
     sign-registration-request   Sign a registration request for this device to be registered at...
 
 FIDO2, U2F and WebAuthN management commands.
diff --git a/python/src/trezorlib/cli/evolu.py b/python/src/trezorlib/cli/evolu.py
index 5768a868..1650d721 100644
--- a/python/src/trezorlib/cli/evolu.py
+++ b/python/src/trezorlib/cli/evolu.py
@@ -114,6 +114,11 @@ def index_management(
     session: Session,
     rotation_index: Optional[int] = None,
 ) -> str:
+    """
+    Read the rotation index for the delegated identity key.
+    If the index is not set and `--rotation_index` is provided, initialize it to that value.
+    Returns the current index, or None if unset.
+    """
     return str(
         evolu.index_management(
             session,