Add Usage and API sections to README

Author: dudik

README.md

@@ -1,4 +1,28 @@
 # adblock-rust-server
 Server wrapper for the [adblock crate](https://crates.io/crates/adblock) using Unix domain sockets.
 
-Created for [blockit](https://github.com/dudik/blockit), but can be used in any program that support Unix domain sockets. Basic documentation will be added soon.
+Created for [blockit](https://github.com/dudik/blockit), but can be used in any program that supports Unix domain sockets.
+
+## Usage
+Add urls of filter lists (e.g. https://easylist.to/easylist/easylist.txt) to `~/.config/ars/urls`.  
+Custom rules (e.g. ###customAd) should be added to `~/.config/ars/lists/custom`.
+
+## API
+After launching adblock-rust-server connect to `/tmp/ars` socket file to start communicating. 
+Every request and response message have to end with a new line character `\n`. Two request types are supported:
+
+### Network request
+`n <request_url> <source_url> <request_type>`
+
+For example:
+`n https://duckduckgo.com/p103.js https://duckduckgo.com/ script`
+
+Checks if the request should be blocked. Returns `1` if it should and `0` if not.
+
+### Cosmetic request
+`c <website_url> <ids> <classes>`
+
+For example:
+`c https://duckduckgo.com/ pg-index   wedonttrack content_homepage    logo_homepage_link`
+
+Returns a CSS rule that hides unwanted elements. `<ids>` and `<classes>` are lists of id/class names separated by the tab character `\t`.