Updated docs.

docs/developers/apps.md

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+# Applications
+
+In `fn`, an application is a group of functions with path mappings (routes) to each function ([learn more](model.md)).
+We've tried to make it easy to work with full applications by providing tools that work with all the applications functions.
+
+## Creating an Application
+
+All you have to do is create a file called `app.yaml` in your applications root directory, and the only required field is a name:
+
+```yaml
+name: myawesomeapp
+```
+
+Once you have that file in place, the `fn` commands will work in the context of that application.
+
+## The Index Function (aka: Root Function)
+
+The root app directory can also contain a `func.yaml` which will be the function access at `/`.
+
+## Function paths
+
+By default, the function name and path will be the same as the directory structure. For instance, if you
+have a structure like this:
+
+```txt
+- app.yaml
+- func.yaml
+- func.go
+- hello/
+  - func.yaml
+  - func.js
+- users/
+  - func.yaml
+  - func.rb
+```
+
+The URL's to access those functions will be:
+
+```
+http://abc.io/ -> root function
+http://abc.io/hello -> function in hello/ directory
+http://abc.io/users -> function in users/ directory
+```
+
+## Deploying an entire app at once
+
+```sh
+fn deploy --all
+```
+
+If you're just testing locally, you can speed it up with the `--local` flag.
+
+## Deploying a single function in the app
+
+To deploy the `hello` function only, from the root dir, run:
+
+```sh
+fn deploy hello
+```
+
+## Example app
+
+See https://github.com/fnproject/fn/tree/master/examples/app for a simple example.