fix: docker support improvements

- Build the binary with Mage.
- Set the ENTRYPOINT to "spruce".
- Add instructions on building and using the docker image.

.dockerignore

@@ -1,5 +0,0 @@
-*
-!*.go
-!templates/*
-!go.mod
-!go.sum

Dockerfile

@@ -1,23 +1,32 @@
 # syntax=docker/dockerfile:1
-FROM golang:1.21-buster AS spruce-builder
+FROM golang:1.21-alpine AS builder
 
 ENV CGO_ENABLED=0
 ENV GOOS=linux
 ENV GOARCH=amd64
 
+WORKDIR /tmp
+
+RUN apk add --no-cache git \
+    && git clone https://github.com/magefile/mage
+
+WORKDIR /tmp/mage
+
+RUN go run bootstrap.go
+
 COPY . /workspace
 
 WORKDIR /workspace
 
-RUN go build -a -v -o /workspace/spruce
+RUN mage build
 
 FROM alpine:3.18
 
-COPY --from=spruce-builder /workspace/spruce /usr/local/bin
+COPY --from=builder /workspace/spruce /usr/local/bin
 
 # Install dependencies
 RUN apk upgrade --no-cache \
-    && apk add \
+    && apk add --no-cache \
          font-carlito \
          aspell \
          curl \
@@ -34,3 +43,5 @@ RUN curl -LO http://lmtx.pragma-ade.com/install-lmtx/context-linuxmusl.zip \
 ENV PATH=${PATH}:/opt/context/tex/texmf-linuxmusl/bin
 
 WORKDIR /workspace
+
+ENTRYPOINT ["spruce"]

README.asciidoc

@@ -57,6 +57,12 @@ The project includes a https://codeflow.dananglin.me.uk/apollo/spruce/src/branch
 With Mage the build information is built into the binary when it is compiled.
 You can visit the https://magefile.org[website] for instructions on how to install Mage.
 
+=== Docker (Optional)
+
+You can use Docker to build and use a docker image built with spruce and ConText installed.
+This could be useful for those who are comfortable using Docker and don't want to install the above dependencies
+directly onto their machines.
+
 == Installation
 
 === With Mage
@@ -87,6 +93,16 @@ cd spruce
 go install .
 ----
 
+=== Building the Docker image
+
+You can build a docker image using the Dockerfile included in this project.
+The build will build and install the spruce binary as well as install all the required dependencies in the final image.
+You can build the docker image with the following command:
+[source,console]
+----
+docker build -t spruce .
+----
+
 === Verifying the installation
 
 Run `spruce` to verify your installation. You should see the usage printed onto your screen.
@@ -112,6 +128,13 @@ Flags:
 Use "spruce [command] --help" for more information about a command.
 ----
 
+If you've build the docker image you can get the same help message with the following command:
+
+[source,console]
+----
+docker run --rm -it spruce
+----
+
 If you have installed spruce with Mage, you can get the build information to confirm that you have installed the correct version.
 [source,console]
 ----
@@ -123,16 +146,30 @@ Spruce
   Build date: 2023-08-12T13:00:51Z
 ----
 
+If you've built the docker image you can verify it with the following command:
+[source,console]
+----
+docker run --rm spruce version --full
+----
+
 == Generating the example PDF Document
 
-Once you've installed spruce you can generate a PDF from the example CV by running the following command:
+Once you've installed spruce you can generate a PDF file from the example CV by running the following command:
 
 [source,console]
 ----
 spruce generate --input example/cv.json
 ----
 
-This will create a file called `cv.pdf` which you can view in your favourite PDF viewer.
+This will create a file called `cv.pdf` which you can view with your favourite PDF viewer.
+
+If you're using the docker image you can generate the PDF file using the following command:
+[source,console]
+----
+docker run --rm -v ./example:/workspace spruce generate --input cv.json --output cv.pdf
+----
+
+The PDF file will be created in the `example` folder.
 
 == Inspirations