Merge branch 'master' into master

Dockerfile.alpine

@@ -8,7 +8,8 @@ RUN apk --update --no-cache add \
     git \
     bash \
     gawk \
-    procps
+    procps \
+    coreutils
 
 COPY ./ /backup-utils/
 WORKDIR /backup-utils

docs/requirements.md

@@ -61,6 +61,8 @@ snapshot of GitHub Enterprise Server 2.11, the target GitHub Enterprise Server a
 be running GitHub Enterprise Server 2.12.x or 2.13.x. You can't restore a snapshot from
 2.10 to 2.13, because that's three releases ahead.
 
+**Note**: You _cannot_ restore a backup created from a newer verison of GitHub Enterprise Server to an older version. For example, an attempt to restore a snapshot of GitHub Enterprise Server 2.21 to a GitHub Enterprise Server 2.20 environment will fail with an error of `Error: Snapshot can not be restored to an older release of GitHub Enterprise Server.`.
+
 [1]: https://www.gnu.org/software/bash/
 [2]: https://git-scm.com/
 [3]: https://www.openssh.com/