Update README to emphasize Rust dependency

Author: mischov

README.md

@@ -5,16 +5,24 @@
 
 A fork of Hansihe's [html5ever_elixir](https://github.com/hansihe/html5ever_elixir) that is more tightly coupled with [Meeseeks](https://github.com/mischov/meeseeks).
 
+## Dependencies
+
+Meeseeks_Html5ever depends on the Rust library [html5ever](https://github.com/servo/html5ever), and you will need to have the Rust compiler [installed](https://www.rust-lang.org/en-US/install.html).
+
 ## Installation
 
-The package can be installed by adding `meeseeks_html5ever` to your list of dependencies in `mix.exs`:
+Ensure Rust is installed, then add Meeseeks_Html5ever to your `mix.exs`:
 
 ```elixir
 def deps do
-  [{:meeseeks_html5ever, "~> 0.6.1"}]
+  [
+    {:meeseeks_html5ever, "~> 0.6.1"}
+  ]
 end
 ```
 
+Finally, run `mix deps.get`.
+
 ## License
 
 Licensed under either of