Add a fallback script to publish docs

Sometimes the github action that runs `sbt publish-website` fails,
this script is a quick workaround to use locally.

website/push-docs.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+# Creates the documentation website and pushes it to the branch
+# 'current-docs' in order to be published.
+#
+# It is a fallback, when `sbt publish-website` is not working due to
+# too large payloads (as it seems) that prohibit uploading through
+# githubs http api. Therefore this script uses git (over ssh).
+
+set -o errexit -o pipefail -o noclobber -o nounset
+
+cdir=$(pwd)
+# make sure we are in source root
+if [ "$cdir" != $(git rev-parse --show-toplevel) ]; then
+    echo "Please go into the source root."
+    exit 1
+fi
+
+# make sure we are on branch 'current-docs'
+branch=$(git branch --show-current)
+if [ "$branch" != "current-docs" ]; then
+    echo "Current branch is not 'current-docs', but $branch."
+    exit 1
+fi
+
+# check for dirty branch
+if [[ -n $(git status -s) ]]; then
+    echo "Working dir is dirty. Abort."
+    exit 1
+fi
+
+temp=$(mktemp -d)
+trap "{ rm -rf '$temp'; }" EXIT
+
+echo "Cloning docspell into new location $temp"
+git clone git@github.com:eikek/docspell.git "$temp"
+cd "$temp" && git checkout --track origin/gh-pages
+
+echo "Create new website from current working directory"
+cd $cdir && nix-shell website/shell.nix --run 'sbt make-website'
+
+echo "Copying new site to target"
+cp -R "$cdir"/website/target/zola-site/* "$temp/"
+
+echo "Showing the diff."
+cd "$temp" && git diff || true
+
+echo "Pushing changes?"
+echo "Use C-c to quit. When continuing, changes are pushed!"
+read
+cd "$temp" && git add . && git commit -am 'Updated gh-pages'  && git push origin gh-pages