docs: tidy up README and user documentation formatting

Author: dido18

README.md

@@ -9,9 +9,11 @@
 [![Test Go status](https://github.com/arduino/arduino-app-cli/actions/workflows/go-test.yml/badge.svg)](https://github.com/arduino/arduino-app-cli/actions/workflows/go-test.yml)
 
 ## Docs
+
 For guidance on installation and development, see the [User documentation].
 
 ## Quickstart
+
 // TODO
 
 ## How to contribute
@@ -23,7 +25,6 @@ contribute your changes to the project.
 
 :sparkles: Thanks to all our [contributors]! :sparkles:
 
-
 ## Security
 
 If you think you found a vulnerability or other security-related bug in the Arduino CLI, please read our [security
@@ -40,9 +41,7 @@ is mandatory if you want to modify or otherwise use the software for commercial
 software without disclosing the source code of your own applications. To purchase a commercial license, send an email to
 license@arduino.cc
 
-
-[user documentation]:  https://github.com/arduino/arduino-app-cli/docs/user-documentation.md
+[user documentation]: https://github.com/arduino/arduino-app-cli/docs/user-documentation.md
 [how to contribute]: https://arduino.github.io/arduino-app-cli/latest/CONTRIBUTING/
 [security policy]: https://github.com/arduino/arduino-app-cli/security/policy
 [contributors]: https://github.com/arduino/arduino-cli/graphs/contributors
-

docs/CONTRIBUTING.md

@@ -1 +1 @@
-## TODO
+## TODO

docs/user-documentation.md

@@ -1,5 +1,5 @@
-
 ## Environment Variables
+
 The following environment variables are used to configure `arduino-app-cli`:
 
 ### Application Directories