Add developer docs

[MichaelCurrin]

Hi,

I managed to get the project setup locally, but it was not straightforward because the docs cover end-users rather than developers.

Can I suggest docs/development.md.

[MichaelCurrin]

Which has something like:

# Development
> Guide for developers working on this project

## Installation

Install Ruby, 

clone repo...

Run `bundle config ...` and `bundle install`


## Usage

Run all unit tests:

```sh
script/test 
```

Run specific unit tests:

```sh
script/test spec/owner_spec.rb
```

Run dev server for sample Jekyll site.

```sh
script/test-site
```

Then open in the browser at

- http://127.0.0.1:4000

And deployment either as a section there or as a short release.md doc. I don't know if more steps are needed but this is what I found.

# Release

```sh
script/release
```

[jekyllbot]

This issue has been automatically marked as stale because it has not been commented on for at least two months.

The resources of the Jekyll team are limited, and so we are asking for your help.

If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open.

If this is a feature request, please consider whether it can be accomplished in another way. If it cannot, please elaborate on why it is core to this project and why you feel more than 80% of users would find this beneficial.

This issue will automatically be closed in two months if no further activity occurs. Thank you for all your contributions.

[MichaelCurrin]

I'll make a PR if no one has the time to.

[jekyllbot]

This issue has been automatically marked as stale because it has not been commented on for at least two months.

The resources of the Jekyll team are limited, and so we are asking for your help.

If this is a bug and you can still reproduce this error on the master branch, please reply with all of the information you have about it in order to keep the issue open.

If this is a feature request, please consider whether it can be accomplished in another way. If it cannot, please elaborate on why it is core to this project and why you feel more than 80% of users would find this beneficial.

This issue will automatically be closed in two months if no further activity occurs. Thank you for all your contributions.

[MichaelCurrin]

PR added. Please review 👀