move BORG_KEY_FILE closer to BORG_KEYS_DIR

docs/usage.rst

@@ -77,8 +77,6 @@ General:
         When set, use the value to answer the passphrase question for encrypted repositories.
     BORG_DISPLAY_PASSPHRASE
         When set, use the value to answer the "display the passphrase for verification" question when defining a new passphrase for encrypted repositories.
-    BORG_KEY_FILE
-        When set, use the given filename as repository key file.
     BORG_LOGGING_CONF
         When set, use the given filename as INI_-style logging configuration.
     BORG_RSH
@@ -103,9 +101,11 @@ Some automatic "answerers" (if set, they automatically answer confirmation quest
     answer or ask you interactively, depending on whether retries are allowed (they by default are
     allowed). So please test your scripts interactively before making them a non-interactive script.
 
-Directories:
+Directories and files:
     BORG_KEYS_DIR
         Default to '~/.config/borg/keys'. This directory contains keys for encrypted repositories.
+    BORG_KEY_FILE
+        When set, use the given filename as repository key file.
     BORG_CACHE_DIR
         Default to '~/.cache/borg'. This directory contains the local cache and might need a lot
         of space for dealing with big repositories).