Add simple readme file with installation instructions

README.md

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+# Neversink filter updater
+
+This is a simple tool for updating of [Neversink's loot filter](https://github.com/NeverSinkDev/NeverSink-Filter).
+
+
+## Installation
+
+* Download the latest version from [release section](https://github.com/ondrowan/neversink-filter-updater/releases).
+* In case you prefer normal style filters, just run the file.
+* In case you wish to use different style of filters:
+    * Create a shortcut of exe file.
+    * Right click it and select "Properties".
+    * In "Shortcut" section, append desired style name behind "Target".
+      Currently, valid choices are: `blue`, `purple`, `slick` and `streamsound`.
+
+This program was tested on 64-bit Windows 10.