[skip changelog]Prevent Prettier from wrapping nightly download link definitions (#901)

Prettier is configured to wrap lines in Markdown files at 120 characters. The reference definitions for the nightly ARM downloads happen to be longer than 120 characters, and so get wrapped.

With the modern Markdown specification, this is permitted:
https://spec.commonmark.org/0.29/#link-reference-definitions

> A link reference definition consists of a link label, indented up to three spaces, followed by a colon (:), optional whitespace (including up to one line ending), a link destination

but apparently the Python-Markdown renderer used by MkDocs does not support this.

The solution is to remove the line breaks and markup to instruct Prettier to ignore these lines:

https://prettier.io/docs/en/ignore.html#markdown

Author: per1234

docs/installation.md

@@ -84,10 +84,12 @@ to get the latest nightly build available for the supported platform, use the fo
 
 [nightly linux 64 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_64bit.tar.gz
 [nightly linux 32 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_32bit.tar.gz
-[nightly linux arm 64 bit]:
-  https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_ARM64.tar.gz
-[nightly linux arm 32 bit]:
-  https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_ARMv7.tar.gz
+
+<!-- prettier-ignore -->
+[nightly linux arm 64 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_ARM64.tar.gz
+
+<!-- prettier-ignore -->
+[nightly linux arm 32 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Linux_ARMv7.tar.gz
 [nightly windows 64 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Windows_64bit.zip
 [nightly windows 32 bit]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_Windows_32bit.zip
 [nightly mac osx]: https://downloads.arduino.cc/arduino-cli/nightly/arduino-cli_nightly-latest_macOS_64bit.tar.gz