Updated docs, cleaned things up, DRY's up function format stuff. (#688)

* Updated docs, cleaned things up, DRY's up function format stuff.

* deleted files

* updated bad link

docs/developers/packaging.md

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+# Packaging your Function
+
+## Option 1 (recommended): Use the `fn` cli tool
+
+We recommend using the [fn cli tool](../fn/README.md) which will handle all of this for you. But if you'd like to dig in
+and customize your images, look at Option 2.
+
+## Option 2: Build your own images
+
+Packaging a function has two parts:
+
+* Create a Docker image for your function with an ENTRYPOINT
+* Push your Docker image to a registry (Docker Hub by default)
+
+Once it's pushed to a registry, you can use the image location when adding a route.
+
+### Creating an image
+
+The basic Dockerfile for most languages is along these lines:
+
+```
+# Choose base image
+FROM node:alpine
+# Set the working directory
+WORKDIR /function
+# Add your binary or code to the working directory
+ADD . /function/
+# Set what will run when a container is started for this image
+ENTRYPOINT ["node func.js"]
+```
+
+Then build your function image:
+
+```sh
+fn build
+```
+
+### Push your image
+
+```sh
+fn push
+```
+
+Now you can use that image when creating or updating routes.