This env vars have been supported for a while, let's document them where
we usually document them.
to expose a single device only, since those identifiers better should be kept
unique.
+`systemd-pcrlock`, `systemd-pcrextend`:
+
+* `$SYSTEMD_MEASURE_LOG_USERSPACE` – the path to the `tpm2-measure.log` file
+ (containing userspace measurement data) to read. This allows overriding the
+ default of `/run/log/systemd/tpm2-measure.log`.
+
+* `$SYSTEMD_MEASURE_LOG_FIRMWARE` – the path to the `binary_bios_measurements`
+ file (containing firmware measurement data) to read. This allows overriding
+ the default of `/sys/kernel/security/tpm0/binary_bios_measurements`.
+
Tools using the Varlink protocol (such as `varlinkctl`) or sd-bus (such as
`busctl`):