add initial readme

README.md

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 # svelte-tiny-spa
+
+A tiny unframework for making SPAs in Svelte.
+
+## Overview
+
+This library intercepts clicks on internal links and turns them into `history.pushState()` calls. The browser's `location` object is exposed through a Svelte store, which updates upon these intercepted clicks or on other `popstate` events. It also optionally provides a mechanism for hosts which do not support falling back to `index.html` for missing files.
+
+## Setup
+
+If your host supports falling back to `index.html` for requests of all unknown files, you should use that feature. Copy [`location.js`](location.js) into your project, and you're done.
+
+### If your host does not support falling back to `index.html`
+
+You'll use a custom 404 page that redirects to the root and encodes the original URL is a query parameter. The root page then rewrites the URL with `history.replaceState()`.
+
+Add [`404.html`](404.html) to your project at the appropriate path. Uncomment the lines at the top of [`location.js`](location.js) to handle the rewrite after the redirection.
+
+## Usage
+
+```js
+import location from '.../location.js';
+```
+
+This is a Svelte store containing the `location` object, and updates whenever a link click is intercepted or a `popstate` event occurs.
+
+Interception occurs when all of the following are met:
+
+1. The link is same-origin
+1. The link does not have a `target` attribute
+1. The link does not have a `download` attribute
+1. The link is left clicked
+1. Ctrl/Cmd/Shift are not pressed when clicking the link
+
+## License
+
+[MIT](LICENSE)