Updated docker installation guide to include UID requirements. (#64)

Author: crc-invisio

docs/installation/docker/index.md

@@ -23,6 +23,8 @@ This article is based on RustFS official Linux binary packages, packaging RustFS
 
  * Define listening port, admin account, data path, etc. in host `/etc/rustfs/config.toml` (see Section 4 for details)
 
+4. RustFS container run as non-root user `rustfs` with id `10001`, if you run docker with `-v` to mount host directory into docker container, please make sure the owner of host directory has been changed to `10001`, otherwise you will encounter permission denied error.
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 ## 2. Quick Pull of RustFS Official Image