Add prerequisites to README.

substratevm/README.md

@@ -7,7 +7,11 @@ Substrate VM is a framework that allows ahead-of-time (AOT) compilation of Java
 
 ## Quick start
 
-Install [mx](https://github.com/graalvm/mx) and point `JAVA_HOME` to a [labsjdk](http://www.oracle.com/technetwork/oracle-labs/program-languages/downloads/index.html). After cloning the repository, run
+Install [mx](https://github.com/graalvm/mx) and point `JAVA_HOME` to a [labsjdk](http://www.oracle.com/technetwork/oracle-labs/program-languages/downloads/index.html).
+
+For compilation `native-image` depends on the local toolchain, so make sure: `glibc-devel`, `zlib-devel` (header files for the C library and `zlib`) and `gcc` are available on your system.
+
+After cloning the repository, run
 
 ```bash
 cd substratevm