Clarify that sh is not required in template install docs

A significant portion of Arduino users use Windows. The first option listed in the installation instructions is for an
installation shell script, which can be used on Windows, but might not be convenient for some Windows users.

This could be discouraging or frustrating to potential new users, but not necessarily so because the script is an
optional convenience and directly downloading and installing the tool is also an option, as documented in the
instructions for the second listed option.

A little refinement of the wording of the script's `sh` requirement makes the situation clear to those users.

Author: per1234

docs/installation.md

@@ -4,8 +4,9 @@ Several options are available for installation of Arduino Lint. Instructions for
 
 ## Use the install script
 
-The script requires `sh`, which is always available on Linux and macOS. `sh` is not available by default on Windows. The
-script can be run on Windows by installing [Git for Windows](https://gitforwindows.org/), then running it from Git Bash.
+The script requires `sh`, which is always available on Linux and macOS. `sh` is not available by default on Windows,
+though it is available as part of [Git for Windows](https://gitforwindows.org/) (Git Bash). If you don't have `sh`
+available, use the ["Download" installation option](#download).
 
 This script will install the latest version of Arduino Lint to `$PWD/bin`: