Clarify install via download

- Clarify executable needs to be renamed to proceed with the getting started section
- Not needed for the build from source section

Author: mcdonnelldean

README.md

@@ -25,6 +25,8 @@ the latest preview version is `0.3.3-alpha.preview`:
 - [Windows](https://downloads.arduino.cc/arduino-cli/arduino-cli-latest-windows.zip)
 - [Mac OSX](https://downloads.arduino.cc/arduino-cli/arduino-cli-latest-osx.zip)
 
+Once downloaded, place the executable into a directory which is in your `PATH` environment variable. To use the tool as it is presented in the Getting started guide below (`arduino-cli`), you should rename the executable from _arduino-cli-0.2.2-alpha.preview-XYZ_ to _arduino-cli_.
+
 ### Build the latest "bleeding-edge" from source
 
 * You should have a recent Go compiler installed.