Merge readme sections about mx

Author: msimacek

README.md

@@ -20,24 +20,25 @@ To try GraalPython with a full GraalVM, including the support for Java embedding
 and interop with other languages, you can use the bundled releases from
 [www.graalvm.org](https://www.graalvm.org/downloads/).
 
-If you want to build GraalPython from source, checkout this repository and the
-[mx](https://github.com/graalvm/mx) build tool, and run `mx --dy /compiler
-python-gvm` in the `graalpython` repository root. If the build is fine, it will
-print the full path to the `graalpython` executable as the last line of output.
-
-For more information and some examples of what you can do with GraalPython,
-check out the [reference](https://www.graalvm.org/reference-manual/python/).
-
-### Create a virtual environment
-#### Requirements:
----
-* [mx](https://github.com/graalvm/mx) - a separate Python tool co-developed for GraalVM development. This tool must be downloaded and put onto your PATH:
+### Building from source
+#### Requirements
 
+* [mx](https://github.com/graalvm/mx) - a separate Python tool co-developed for GraalVM development. This tool must be
+  downloaded and put onto your PATH:
 ```
 git clone https://github.com/graalvm/mx.git
 export PATH=$PWD/mx:$PATH
 ```
----
+
+#### Building
+
+Run `mx --dy /compiler python-gvm` in the `graalpython` repository root. If the build is fine, it will print the full
+path to the `graalpython` executable as the last line of output.
+
+For more information and some examples of what you can do with GraalPython,
+check out the [reference](https://www.graalvm.org/reference-manual/python/).
+
+### Create a virtual environment
 The best way of using the GraalVM implementation of Python is out of a virtual environment. To do so
 execute the following command in the project directory: