docs and README: add wacz format doc, tweak links, tweak README

docs/wacz-format.md

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+---
+layout: default
+title: 'Web Archive Collection Zipped (WACZ) Format'
+nav_order: 1
+permalink: /docs/wacz-format
+parent: Reference
+---
+
+## Web Archive Collection Format Specification
+
+ReplayWeb.page supports a new format for bundling raw web archive data (usually WARC files), indices,
+page lists and other metadata into a single ZIP file.
+
+The full spec for this format is available at: [https://github.com/webrecorder/web-archive-collection-format/blob/master/README.md](https://github.com/webrecorder/web-archive-collection-format/blob/master/README.md)
+
+Files bundled into this format can use the .wacz (web archive collection zipped) file extension.
+
+ReplayWeb.page will recognize this extension (as well as regular .zip) and will also load it from Google Drive when the
+[Google Drive Integration](https://gsuite.google.com/u/2/marketplace/app/replaywebpage/160798412227) is installed.
+
+The key benefit of this format is that large web archive collections can be loaded very quickly, to show the page list
+and other key metadata, by downloading only parts of the WACZ file, as [outlined here](https://github.com/webrecorder/web-archive-collection-format/blob/master/README.md#appendix-a-use-case-random-access-to-web-archives-in-zip)
+
+The actual raw content is loaded on-demand when the user requests each page.
+
+With a WARC file, the entire contents must be loaded or indexed to determine the contents of the web archive collection.