Add README

README.md

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+# Procreate Viewer
+I use my computer to store all of my backups of my [Procreate](https://procreate.art) documents (since they seem reluctant to add actual cloud saving), but
+I can never figure out which documents are which, so I created this app to alleviate this dilemma.
+
+This app contains a document-based viewer that associates itself with the `.procreate` file format. It also contains a Quick Look
+preview and thumbnail generator, all written in Swift and Cocoa. Please note that since there is almost no documentation on how
+these new generator api's work, they might be broken.
+
+This app uses the Swift Package Manager to handle our sole dependency, [ZipFoundation](https://github.com/weichsel/ZIPFoundation).
+
+## Procreate File Format
+All `.procreate` files are actually standard ZIP files. So extracting them leads to something like this:
+```
+- (Multiple folders named randomly via UUID)
+  - Contains .chunk files, presumably the actual pixel canvas data for the document.
+- QuickLook [Folder]
+  - Thumbnail.png - Low-quality screenshot generated by Procreate.
+- video [Folder]
+  - segments [Folder]
+    - segment-X.mp4, where X is a number starting from 1. These are most likely the timelapse files.
+- Document.archive - ???
+```
+
+We simply extract the zip file in memory, and display the `Thumbnail.png` found in the file. Notice how I said these thumbnails are
+'low-quality', and even though they may seem low-quality when blown up on a Retina display like most iPads, these tend to be more
+than servicable for thumbnail usage.