Replace unsupported definition list syntax in README.md (#689)

* Replace unsupported definition list syntax in README.md

problem: GitHub Flavored Markdown (GFM) does not support Markdown's definition lists natively.

fix: simulate a definition list using bold terms and line breaks

* Update README.md

* Add line breaks in README.md

Author: emig

README.md

@@ -18,20 +18,17 @@ is favored as of now.
 
 #### Features
 
-Safety
-: The code you write in a Rust NIF should never be able to crash the BEAM.
+**Safety**  
+The code you write in a Rust NIF should never be able to crash the BEAM.
 
-Interop
-: Decoding and encoding rust values into Erlang terms is as easy as a function
-: call.
+**Interop**  
+Decoding and encoding rust values into Erlang terms is as easy as a function call.
 
-Type composition
-: Making a Rust struct encodable and decodable to Erlang or Elixir can be done
-: with a single attribute.
+**Type composition**  
+Making a Rust struct encodable and decodable to Erlang or Elixir can be done with a single attribute.
 
-Resource objects
-: Enables you to safely pass a reference to a Rust struct into Erlang code. The
-: struct will be automatically dropped when it's no longer referenced.
+**Resource objects**  
+Enables you to safely pass a reference to a Rust struct into Erlang code. The struct will be automatically dropped when it's no longer referenced.
 
 #### Getting started