enable github-based npm packages for WIKI_PACKAGE

npm needs git installed in order to install packages from github

Dockerfile

@@ -3,7 +3,8 @@ FROM node:4-slim
 RUN useradd --create-home app \
  && apt-get update \
  && apt-get install -y --no-install-recommends \
-    jq
+    jq \
+    git
 WORKDIR /home/app
 ARG WIKI_PACKAGE=wiki@0.12.1
 RUN su app -c "npm install -g --prefix . $WIKI_PACKAGE"

README.md

@@ -52,8 +52,11 @@ Open http://that.localtest.me:3000 in another.
 
 # Development
 
+This image's tag matches the version of the included wiki software.
+
 ``` bash
-VERSION=0.12.0
-docker build --build-arg VERSION=$VERSION -t dobbs/farm:$VERSION .
-git tag -am "" $VERSION
+git tag -am "" '0.12.1+github'
+git push --tags
+docker build -t dobbs/farm:0.12.1+github .
+docker push dobbs/farm:0.12.1+github
 ```