docs: document new mount option env var

diff --git a/docs/ENVIRONMENT.md b/docs/ENVIRONMENT.md
index 2c61935b6bbf9117f89148dfef4b66183ef4b3d2..5f783ed9155a639e3b13e9d211869a2df8d253c2 100644 (file)
--- a/docs/ENVIRONMENT.md
+++ b/docs/ENVIRONMENT.md
@@ -433,3 +433,9 @@ SYSTEMD_HOME_DEBUG_SUFFIX=foo \
       SYSTEMD_HOME_RECORD_DIR=/var/lib/systemd/home.foo/ \
       /home/lennart/projects/systemd/build/systemd-homed
 ```
+
+* `$SYSTEMD_HOME_MOUNT_OPTIONS_BTRFS`, `$SYSTEMD_HOME_MOUNT_OPTIONS_EXT4`,
+  `$SYSTEMD_HOME_MOUNT_OPTIONS_XFS` – configure the default mount options to
+  use for LUKS home directories, overriding the built-in default mount
+  options. There's one variable for each of the supported file systems for the
+  LUKS home directory backend.