Add "key import" to reference documentation (#345).

docs/Dockerfile

@@ -4,7 +4,7 @@ COPY . /app
 RUN apk add --no-cache py3-pip py3-ruamel.yaml py3-ruamel.yaml.clib
 RUN pip install --break-system-packages --no-cache /app && borgmatic config generate && chmod +r /etc/borgmatic/config.yaml
 RUN borgmatic --help > /command-line.txt \
-    && for action in repo-create transfer create prune compact check delete extract config "config bootstrap" "config generate" "config validate" export-tar mount umount repo-delete restore repo-list list repo-info info break-lock "key export" "key change-passphrase" borg; do \
+    && for action in repo-create transfer create prune compact check delete extract config "config bootstrap" "config generate" "config validate" export-tar mount umount repo-delete restore repo-list list repo-info info break-lock "key export" "key import" "key change-passphrase" borg; do \
            echo -e "\n--------------------------------------------------------------------------------\n" >> /command-line.txt \
            && borgmatic $action --help >> /command-line.txt; done
 RUN /app/docs/fetch-contributors >> /contributors.html