Clean up Linux build instructions (#2580)

Author: devsaurus

docs/en/build.md

@@ -9,7 +9,14 @@ NodeMCU "application developers" just need a ready-made firmware. There's a [clo
 Occasional NodeMCU firmware hackers don't need full control over the complete tool chain. They might not want to setup a Linux VM with the build environment. Docker to the rescue. Give [Docker NodeMCU build](https://hub.docker.com/r/marcelstoer/nodemcu-build/) a try.
 
 ### Linux Build Environment
-NodeMCU firmware developers commit or contribute to the project on GitHub and might want to build their own full fledged build environment with the complete tool chain. There is a [post in the esp8266.com Wiki](http://www.esp8266.com/wiki/doku.php?id=toolchain#how_to_setup_a_vm_to_host_your_toolchain) that describes this.
+NodeMCU firmware developers commit or contribute to the project on GitHub and might want to build their own full fledged build environment with the complete tool chain. The NodeMCU project embeds a [ready-made tool chain](https://github.com/nodemcu/nodemcu-firmware/blob/401fa56b863873c4cbf0b6581eb36fc61046ff6c/Makefile#L225) for Linux/x86-64 by default. After working through the [Build Options](#build-options) below, simply start the build process with
+```
+make
+```
+
+!!! note
+
+    Building the tool chain from scratch is out of NodeMCU's scope. Refer to [ESP toolchains](https://github.com/jmattsson/esp-toolchains) for related information.
 
 ### Git
 If you decide to build with either the Docker image or the native environment then use Git to clone the firmware sources instead of downloading the ZIP file from GitHub. Only cloning with Git will retrieve the referenced submodules: