Move installation script to etc subfolder

I would prefer to avoid cluttering up the root of the repository too much. The reason is that when people visit the
repository on GitHub, they must scroll down past the root directory listing before getting to the readme. Some files and
folders must be in the root, but there are some others (e.g., gon.config.hcl) that can be moved to a subfolder, so this
move can be part of a larger campaign.

Author: per1234

Diff for: docs/installation.md

@@ -6,13 +6,13 @@ script can be run on Windows by installing [Git for Windows](https://gitforwindo
 This script will install the latest version of arduino-lint to `$PWD/bin`:
 
 ```
-curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/install.sh | sh
+curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/install.sh | sh
 ```
 
 If you want to target a different directory, for example `~/local/bin`, set the `BINDIR` environment variable like this:
 
 ```
-curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/install.sh | BINDIR=~/local/bin sh
+curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/install.sh | BINDIR=~/local/bin sh
 ```
 
 If you would like to use the `arduino-lint` command from any location, install arduino-lint to a directory already in
@@ -22,7 +22,7 @@ If you want to download a specific arduino-lint version, for example `0.9.0`, pa
 like this:
 
 ```
-curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/install.sh | sh -s 0.9.0
+curl -fsSL https://raw.githubusercontent.com/arduino/arduino-lint/main/etc/install.sh | sh -s 0.9.0
 ```
 
 ### Download