Add README for docs.

doc/README.md

@@ -0,0 +1,41 @@
+The Rhai Book
+=============
+
+[_The Rhai Book_](https://schungx.github.io/rhai) serves as Rhai's primary
+documentation and tutorial resource.
+
+
+How to Build from Source
+------------------------
+
+* Install [`mdbook`](https://github.com/rust-lang/mdBook):
+
+```bash
+cargo install mdbook
+```
+
+* Install [`mdbook-tera`](https://github.com/avitex/mdbook-tera) (for templating):
+
+```bash
+cargo install mdbook-tera
+```
+
+* Run build in source directory:
+
+```bash
+cd doc
+mdbook build
+```
+
+
+Configuration Settings
+----------------------
+
+Settings stored in `context.json`:
+
+| Setting    | Description                                                                                       |
+| ---------- | ------------------------------------------------------------------------------------------------- |
+| `version`  | version of Rhai                                                                                   |
+| `repoHome` | points to the [root of the GitHub repo](https://github.com/jonathandturner/rhai/blob/master)      |
+| `repoTree` | points to the [root of the GitHub repo tree](https://github.com/jonathandturner/rhai/tree/master) |
+| `rootUrl`  | sub-directory for the root domain, e.g. `/rhai`                                                   |