Improve installation documentation and add contributor instructions

CONTRIBUTING.md

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+* http://www.ruby-lang.org/ - The homepage of Ruby which has more links and some great tutorials.
+* http://rubyonrails.org/ - The homepage of Rails, also has links and tutorials
+
+## Coding style
+
+When writing code it is generally a good idea to try and match your
+formatting to that of any existing code in the same file, or to other
+similar files if you are writing new code. Consistency of layout is
+far more important that the layout itself as it makes reading code
+much easier.
+
+One golden rule of formatting -- please don't use tabs in your code
+as they will cause the file to be formatted differently for different
+people depending on how they have their editor configured.
+
+## Testing
+
+Having a good suite of tests is very important to the stability and
+maintainability of any code base. The tests in the Rails port code are
+by no means complete, but they are extensive, and must continue to be
+so with any new functionality which is written. Tests are also useful
+in giving others confidence in the code you've written, and can
+greatly speed up the process of merging in new code.
+
+When hacking, you should:
+
+* Write new tests to cover the new functionality you've added.
+* Where appropriate, modify existing tests to reflect new or changed
+functionality.
+* Never comment out or remove a test just because it doesn't pass.
+
+You can run the existing test suite with:
+
+```
+bundle exec rake test
+```
+
+You can generate test coverage stats with:
+
+```
+sudo gem install rcov
+rcov -x gems test/*/*.rb
+```
+
+The tests are automatically run on commit with the results shown at [http://cruise.openstreetmap.org/](http://cruise.openstreetmap.org/)
+
+## Comments
+
+Sometimes it's not apparent from the code itself what it does, or,
+more importantly, **why** it does that. Good comments help your fellow
+developers to read the code and satisfy themselves that it's doing the
+right thing.
+
+When hacking, you should:
+
+* Comment your code - don't go overboard, but explain the bits which
+might be difficult to understand what the code does, why it does it
+and why it should be the way it is.
+* Check existing comments to ensure that they are not misleading.
+
+## Code Documentation
+
+To generate the HTML documentation of the API/rails code, run the command
+
+```
+rake doc:app
+```
+
+## Committing
+
+When you submit patches, the project maintainer has to read them and
+understand them. This is difficult enough at the best of times, and
+misunderstanding patches can lead to them being more difficult to
+merge. To help with this, when submitting you should:
+
+* Split up large patches into smaller units of functionality.
+* Keep your commit messages relevant to the changes in each individual
+unit.
+
+When writing commit messages please try and stick to the same style as
+other commits, namely:
+
+* A one line summary, starting with a capital and with no full stop.
+* A blank line.
+* Full description, as proper sentences with capitals and full stops.
+
+For simple commits the one line summary is often enough and the body
+of the commit message can be left out.
+
+## Sending the patches
+
+If you have forked on GitHub then the best way to submit your patches is to
+push your changes back to GitHub and then send a "pull request" on GitHub.
+
+Otherwise you should either push your changes to a publicly visible git repository
+and send the details to the [rails-dev](http://lists.openstreetmap.org/listinfo/rails-dev)
+list or generate patches with `git format-patch` and send them to the
+[rails-dev](http://lists.openstreetmap.org/listinfo/rails-dev) list.
+