Update README (#27)

Closes #26 

README.md

@@ -2,15 +2,19 @@
 
 Keep npm dependencies up-to-date via Pull Requests
 
+## What does it do?
+
+This script scans your repository package.json files, detects if any dependencies need version updating - or pinning - and if so then submits Pull Requests for each.
+
 ## Before you Start
 
-To run this script, you will need to select a GitHub account for it to use. The account will need read/write access to push and update upgrade branches to GitHub, as well as raise Pull Requests.
+To run this script, you will need to select a GitHub user account for it to create branches and submit Pull Requests from. The account will need read/write access to push and update upgrade branches to GitHub, as well as raise Pull Requests.
 
-We recommend using a "bot" account so that it's clear to other users of the repository that these are automated actions and not a team member performing them all manually.
+We recommend you consider using a "bot" account for this so that it's clear to other users of the repository that these are automated actions and not not confused with an actual team member's actions.
 
-The script will need a GitHub "access token" for authenticating API access. You can find instructions for generating it here: https://help.github.com/articles/creating-an-access-token-for-command-line-use/
+The script will need a GitHub Personal Access Token with "repo" permissions. You can find instructions for generating it here: https://help.github.com/articles/creating-an-access-token-for-command-line-use/
 
-This token needs to be exposed via the environment variable `RENOVATE_TOKEN`.
+This token needs to be exposed via the environment variable `RENOVATE_TOKEN` or added to a configuration file.
 
 ## Running the Script
 
@@ -21,7 +25,7 @@ First, install dependencies for this script by running `npm install`.
  The script can then be run like this:
 
 ```sh
-node src <username>/<repo> <path to package.json>
+npm start <username>/<repo> <path to package.json>
 ```
 
 The `<path to package.json>` argument is optional, and is only needed if your `package.json` is located somewhere other than the root of the repository.
@@ -29,17 +33,46 @@ The `<path to package.json>` argument is optional, and is only needed if your `p
 Example of running with default `package.json` location:
 
 ```sh
-node src singapore/renovate
+npm start foo/bar
 ```
 
 Example of running with a custom `package.json` location:
 
 ```sh
-node src singapore/renovate containers/build/package.json
+npm start foo/bar src/package.json
 ```
 
 Note: as mentioned above, you need to expose the environment variable `RENOVATE_TOKEN`. One way of doing it is like this:
 
 ```sh
-RENOVATE_TOKEN=JDSUW284HSJDSFKSUS22942H2H15KK node src singapore/renovate
+RENOVATE_TOKEN=JDSUW284HSJDSFKSUS22942H2H15KK npm start foo/bar
+```
+
+## Configuration file
+
+It's also possible to configure renovate with a `config.js` file in the working directory. Here is an example:
+
+```js
+module.exports = {
+  token: 'JDSUW284HSJDSFKSUS22942H2H15KK',
+  logLevel: 'verbose',
+  repositories: [
+    'foo/bar',
+    'foo/baz',
+    {
+      name: 'foo/lint',
+      packageFiles: [
+        'package.json',
+        'containers/build/package.json',
+      ],
+    },
+    'foo/package-go',
+  ],
+};
 ```
+
+As you can hopefully infer from the above, it's possible to define multiple repositories as well as multiple package files per repository, and they will be processed in sequence.
+
+If you configure the token and at least one repository in your `config.js` then you don't need any CLI arguments and can just run `npm start`.
+
+It's also possible to change the string templates used for generating branch names, commit messages, and Pull Request titles and body. To override the defaults, copy/paste/edit the templates from `app/config/defaults.js` into your `config.js`. You must copy all of them, even if you only edit one.