advertise jill.py in Downloads as a command-line installation tool (#926

)

* advertise jill.py in Downloads as a command-line installation tool

jill.py is a command-line tool (written in Python) that downloads and
extracts official binaries, and makes symlinks for all platforms.

This could serve as a recommended alternatives to package managers such
as `apt`, `brew` and `choco`

* move jill.py after linux and freebsd section

downloads/platform.md

@@ -103,7 +103,9 @@ Apart from this, there are several ways through which you can change environment
 
 Julia installs all its files in a single directory. Deleting the directory where Julia was installed is sufficient. If you would also like to remove your packages, remove `~/.julia`. The startup file is at `~/.julia/config/startup.jl` and the history at `~/.julia/logs/repl_history.jl`.
 
+## Cross-platform installer
 
+[Jill.py](https://github.com/johnnychen94/jill.py) is a community-maintained command-line tool that automates the installation workflow for all platforms. After installing this using `pip install jill -U`, you can then use `jill install` to install the current stable release, and `jill install latest` to install the nightly builds.
 
 # Platform Specific Instructions for Unofficial Binaries