Add Dockerfile and Compose file to build slides

Fixes #426

slides/Dockerfile

@@ -0,0 +1,7 @@
+FROM alpine
+RUN apk update
+RUN apk add entr
+RUN apk add py-pip
+RUN apk add git
+COPY requirements.txt .
+RUN pip install -r requirements.txt

slides/README.md

@@ -34,6 +34,14 @@ compile each `foo.yml` file into `foo.yml.html`.
 You can also run `./build.sh forever`: it will monitor the current
 directory and rebuild slides automatically when files are modified.
 
+If you have problems running `./build.sh` (because of
+Python dependencies or whatever),
+you can also run `docker-compose up` in this directory.
+It will start the `./build.sh forever` script in a container.
+It will also start a web server exposing the slides
+(but the slides should also work if you load them from your
+local filesystem).
+
 
 ## Publishing pipeline
 
@@ -53,4 +61,4 @@ You can run `./slidechecker foo.yml.html` to check for
 missing images and show the number of slides in that deck.
 It requires `phantomjs` to be installed. It takes some
 time to run so it is not yet integrated with the publishing
-pipeline.
+pipeline.

slides/docker-compose.yaml

@@ -0,0 +1,16 @@
+version: "2"
+
+services:
+  www:
+    image: nginx
+    volumes:
+    - .:/usr/share/nginx/html
+    ports:
+    - 80
+  builder:
+    build: .
+    volumes:
+    - ..:/repo
+    working_dir: /repo/slides
+    command: ./build.sh forever
+