Initial attempt at documentation

[bengreenier]

My first pass at documentation, enabling the following scenarios:

• Readme docs
• Hero image
• Issue templating
• Extension list

Pending items:

• [x] bring in OpenAPI docs
• [x] clarify the extensions are language agnostic
• [x] clarify that this sdk is for node

[bengreenier]

need to include the OpenAPI docs for the expected interface somewhere here.

[bengreenier]

could add an FAQ to cover "i don't use node, [how] can i make chaos extensions?"