Docker image: add support for SYNAPSE_DATA_DIR parameter

Fixes #4830.

1 files changed, 4 insertions, 0 deletions

diff --git a/docker/README.md b/docker/README.md

index 10af88844b..5c85c538a8 100644
--- a/docker/README.md
+++ b/docker/README.md
@@ -186,3 +186,7 @@ The following environment variables are supported in this mode:
 * `SYNAPSE_REPORT_STATS` (mandatory, `yes` or `no`): whether to enable
   anonymous statistics reporting.
 * `SYNAPSE_CONFIG_PATH` (mandatory): path to the file to be generated.
+* `SYNAPSE_DATA_DIR`: where the generated config will put persistent data
+  such as the datatase and media store. Defaults to `/data`.
+* `UID`, `GID`: the user id and group id to use for creating the data
+  directories. Defaults to `991`, `991`.