Concrete examples to supplement(s) when talk about some operation or explanation

Question

I am confused with the usage of the word supplement.

A similar usage might be

a 16-page advertising supplement

where it means

an additional part of a book, newspaper, report etc

Following is the example to illustrate the question.

Here are some steps to copy/paste some content from web browser to a text editor.

1. select the content on the web browser 
2. ctrl + C
3. click the text editor
4. ctrl + V

In this context, is following expressions appropriate?

Here are 2 supplements
1. for Mac user, ...
2. for Linux user,...

Another example

I asked a question

What does "⇒𝑦" mean?

...

then I add a supplement

according to @Joe's answer, ⇒𝑦 is called the “always positive” classifier in the book

...

Could this be A supplement?

Answer 1

1. In this context, are the following expressions appropriate?

In that specific context, even though "supplements" does fit the dictionary definition, the more common expression would be "additional information" or "additional instructions". If the instructions for Mac or Linux are notably different, then it should be "alternate" or "alternative" instead of "additional".

2. could this be a supplement?

Yes. It follows the first definition of "something that you add to something else to improve it or make it complete", and it seems appropriate for that usage.