Include sub-command help in documentation.

docs/Dockerfile

@@ -2,7 +2,10 @@ FROM python:3.7.3-alpine3.9 as borgmatic
 
 COPY . /app
 RUN pip install --no-cache /app && generate-borgmatic-config && chmod +r /etc/borgmatic/config.yaml
-RUN borgmatic --help > /command-line.txt
+RUN borgmatic --help > /command-line.txt \
+    && for action in init prune create check extract list info; do \
+           echo -e "\n--------------------------------------------------------------------------------\n" >> /command-line.txt \
+           && borgmatic "$action" --help >> /command-line.txt; done
 
 FROM node:11.15.0-alpine as html
 

docs/reference/command-line.md

@@ -3,7 +3,8 @@ title: borgmatic command-line reference
 ---
 ## borgmatic options
 
-Here are all of the available borgmatic command-line options:
+Here are all of the available borgmatic command-line options. This includes the separate options for
+each action sub-command:
 
 ```
 {% include borgmatic/command-line.txt %}