docs: add python pre-requisites

Signed-off-by: Miguel Molina <miguel@erizocosmi.co>

README.md

@@ -58,10 +58,16 @@ Either in case the `LANG` variable wouldn't be set to a UTF-8 encoding or it wou
 # Pre-requisites
 
 * Scala 2.11.x
-* Python >= 3.4.x (engine is tested with Python 3.4, 3.5 and 3.6 and these are the supported versions, even if it might still work with previous ones)
 * [Apache Spark Installation](http://spark.apache.org/docs/2.2.1/) 2.2.x or 2.3.x
 * [bblfsh](https://github.com/bblfsh/bblfshd) >= 2.5.0: Used for UAST extraction
 
+## Python pre-requisites:
+
+* Python >= 3.4.x (engine is tested with Python 3.4, 3.5 and 3.6 and these are the supported versions, even if it might still work with previous ones)
+* `libxml2-dev` installed
+* `python3-dev` installed
+* `g++` installed
+
 # Examples of engine usage
 
 **engine** is available on [maven central](https://search.maven.org/#search%7Cga%7C1%7Ctech.sourced.engine). To add it to your project as a dependency,