Image labels (#9)

* Add container description label

Signed-off-by: Dan Webb <dan.webb@damacus.io>

* Add image url and authors label

Signed-off-by: Dan Webb <dan.webb@damacus.io>

Dockerfile

@@ -1,11 +1,18 @@
 FROM python:slim
 
-RUN pip install yamllint
-ENV MATCHERS_DIR="._actionshub_problem-matchers"
-ENV MATCHER_FILE="${MATCHERS_DIR}/yamllint.json"
+LABEL org.opencontainers.image.description \
+  "Yamllint Action for GitHub Actions" \
+  org.opencontainers.image.url \
+  "https://github.com/actionshub/yamllint" \
+  org.opencontainers.image.authors \
+  "https://github.com/actionshub"
+
+ENV MATCHERS_DIR="._actionshub_problem-matchers" \
+  MATCHER_FILE="${MATCHERS_DIR}/yamllint.json"
 
-RUN mkdir -p ${MATCHERS_DIR}
 COPY yamllint.json ${MATCHER_FILE}
-RUN echo "::[add-matcher]${MATCHER_FILE}"
+RUN pip install yamllint \
+  && mkdir -p ${MATCHERS_DIR} \
+  && echo "::[add-matcher]${MATCHER_FILE}"
 
 ENTRYPOINT ["yamllint",".", "--format", "github"]