Docs on writing functions and the functions format. (#203)

* WIP on writing functions and the functions format.

* Added more docs on writing functions.

* Running on windows docs.

* Linked README to writing.md

* Minor fixes from PR feedback.

docs/writing.md

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+# Writing Functions
+
+This will give you the basic overview of writing base level functions. You can also use higher level abstractions that make it easier such
+as [lambda](lambda.md).
+
+## Code
+
+The most basic code layout in any language is as follows, this is pseudo code and is not meant to run.
+
+```ruby
+# Read and parse from STDIN
+body = JSON.parse(STDIN)
+
+# Do something
+return_struct = doSomething(body)
+
+# Respond if sync: 
+STDOUT.write(JSON.generate(return_struct))
+# or update something if async
+db.update(return_struct)
+```
+
+## Inputs 
+
+Inputs are provided through standard input and environment variables. We'll just talk about the default input format here, but you can find others [here](function-format.md). 
+To read in the function body, just read from STDIN. 
+
+You will also have access to a set of environment variables. 
+
+* REQUEST_URL - the full URL for the request
+* ROUTE - the matched route
+* METHOD - the HTTP method for the request
+* CONFIG_X - any configuration values you've set for the Application or the Route. Replace X with the upper cased name of the config variable you set. 
+* HEADER_X - the HTTP headers that were set for this request. Replace X with the upper cased name of the header and replace dashes in the header with underscores. 
+
+Warning: these may change before release.
+
+## Logging
+
+Standard out is where you should write response data for synchronous functions. Standard error 
+is where you should write for logging, as [it was intended](http://www.jstorimer.com/blogs/workingwithcode/7766119-when-to-use-stderr-instead-of-stdout). 
+
+So to write output to logs, simply log to STDERR. Here are some examples in a few languages. 
+
+In Go, simply use the [log](https://golang.org/pkg/log/) package, it writes to STDERR by default. 
+
+```go
+log.Println("hi")
+```
+
+In Node.js:
+
+```node
+console.error("hi");
+```
+
+[More details for Node.js here](http://stackoverflow.com/a/27576486/105562).
+
+In Ruby:
+
+```ruby
+STDERR.puts("hi")
+```
+
+## Packaging
+
+Packaging a function is essentially just creating a Docker image for your function with an ENTRYPOINT.
+
+The basic Dockerfile for most languages is something like this:
+
+```
+# Choose base image
+FROM iron/go
+# Set th working directory
+WORKDIR /function
+# Add your binary or code to the working directory
+ADD hello /function/
+# Set what will run when a container is started for this image
+ENTRYPOINT ["./hello"]
+```
+