[skip ci] Update nightly links and add nightly checksum link (#328)

Author: rsora

README.md

@@ -40,14 +40,21 @@ Alternatively you can download one of the pre-built binaries for the supported p
 
 ### Download a nightly build
 
-These builds are generated once a day from `master` branch starting at 23:00 UTC
-
-- [Linux 64 bit](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-linux64.tar.bz2)
-- [Linux 32 bit](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-linux32.tar.bz2)
-- [Linux ARM 64 bit](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-linuxarm32.tar.bz2)
-- [Linux ARM 32 bit](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-linuxarm64.tar.bz2)
-- [Windows](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-windows.zip)
-- [Mac OSX](https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli-nightly-latest-macosx.zip)
+These builds are generated once a day from `master` branch starting at 01:00 GMT
+
+In order to get the latest nightly build for your platform use the following links replacing `<DATE>` with the current 
+date, using the format YYYYMMDD (i.e for 2019/Aug/06 use `20190806` )
+
+- **Linux 64 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Linux_64bit.tar.gz`
+- **Linux 32 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Linux_32bit.tar.gz`
+- **Linux ARM 64 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Linux_ARM64.tar.gz`
+- **Linux ARM 32 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Linux_ARMv7.tar.gz`
+- **Windows 64 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Windows_64bit.zip`
+- **Windows 32 bit**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_Windows_32bit.zip`
+- **Mac OSX**: `https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-<DATE>_macOS_64bit.tar.gz`
+
+Checksums for the nightly builds are available at 
+`https://downloads.arduino.cc/arduino-cli/nightly/nightly-<DATE>-checksums.txt`
 
 Once downloaded, place the executable `arduino-cli` into a directory which is in your `PATH`.