Reformat, rearrange, and edit install guide

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Created by MOE: https://github.com/google/moe
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docs/developing.md

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 # Developing
 
-Advice on how to do development on the Domain Registry codebase, including how
-to set up an IDE environment and run tests.
+This document contains advice on how to do development on the Nomulus codebase,
+including how to set up an IDE environment and run tests.
+
+## Running a local development server
+
+`RegistryTestServer` is a lightweight test server for the registry that is
+suitable for running locally for development. It uses local versions of all
+Google Cloud Platform dependencies, when available. Correspondingly, its
+functionality is limited compared to a Domain Registry instance running on an
+actual App Engine instance. It is most helpful for doing web UI development such
+as on the registrar console: it allows you to update JS, CSS, images, and other
+front-end resources, and see the changes instantly simply by refreshing the
+relevant page in your browser.
+
+To see the registry server's command-line parameters, run:
+
+```shell
+$ bazel run //javatests/google/registry/server -- --help
+```
+
+To start an instance of the server, run:
+
+```shell
+$ bazel run //javatests/google/registry/server {your params}
+```
+
+Once it is running, you can interact with it via normal `nomulus` commands, or
+view the registrar console in a web browser by navigating to
+[http://localhost:8080/registrar](http://localhost:8080/registrar). The server
+will continue running until you terminate the process.
+
+If you are adding new URL paths, or new directories of web-accessible resources,
+you will need to make the corresponding changes in `RegistryTestServer`. This
+class contains all of the routing and static file information used by the local
+development server.