Update README

README.md

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-# synit
+# SYNIT: A Reactive Operating System
 
-<https://synit.org/>
+ - Homepage: <https://synit.org/>
+ - See also: <https://syndicate-lang.org/projects/2021/system-layer/>
 
-<https://syndicate-lang.org/projects/2021/system-layer/>
+Synit is an experiment in applying **pervasive reactivity** and **object capabilities** to the
+[System Layer](https://synit.org/book/glossary.html#system-layer) of an operating system for
+personal computers, including laptops, desktops, and mobile phones. Its
+[architecture](https://synit.org/book/architecture.html) follows the principles of the
+[Syndicated Actor Model](https://synit.org/book/glossary.html#syndicated-actor-model).
+
+Synit builds upon the Linux kernel, but replaces many pieces of
+familiar Linux software, including `systemd`, `NetworkManager`,
+`D-Bus`, and so on. It makes use of many concepts that will be
+familiar to Linux users, but also incorporates many ideas drawn from
+programming languages and operating systems not closely connected with
+Linux's Unix heritage.
+
+## Quickstart
+
+If you have a mobile phone or computer capable of running
+[PostmarketOS](https://postmarketos.org/), then you can [install](https://synit.org/book/install.html)
+the software to try it out. You can also run Synit inside a virtual machine.
+
+See the [installation instructions](https://synit.org/book/install.html) for a list of supported
+devices.
+
+# Documentation
+
+See [the Synit Manual](https://synit.org/book/).