[Feature] Add README, screenshots and LICENSE.

Author: zhanghai

LICENSE

@@ -1,3 +1,41 @@
-# Material Files
+# Material Files (Beta)
 
-A Material Design file manager.
+A Material Design file manager, for Android 5.0+.
+
+## Preview
+
+<p><img src="screenshots/main.png" width="32%" /> <img src="screenshots/drawer.png" width="32%" /> <img src="screenshots/properties-basic.png" width="32%" />
+<img src="screenshots/settings.png" width="32%" /> <img src="screenshots/standard-directories.png" width="32%" /> <img src="screenshots/about.png" width="32%" /></p>
+
+## Features
+
+- Open source: Lightweight, clean and secure.
+- Material Design: Like the good old [Cabinet](https://github.com/aminb/cabinet), also with dark mode.
+- Breadcrumbs: Navigate in the filesystem with ease.
+- Linux-aware: Like [Nautilus](https://wiki.gnome.org/action/show/Apps/Files), knows symbolic links, file permissions and SELinux context.
+- Robust: Uses Linux syscalls under the hood, not yet another [`ls` parser](https://news.ycombinator.com/item?id=7994720).
+- Well-implemented: Built upon the right things, including Java NIO2 File API and LiveData.
+
+## Things not yet in Beta 1...
+
+- Search files.
+- Extracting archives.
+- File operations with root.
+- More in [Issues](https://github.com/zhanghai/MaterialFiles/issues).
+
+## License
+
+    Copyright (C) 2018 Hai Zhang
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.