Documentation: The Basics―First Start assumes desktop icon and presence in `PATH`

The documentation's _The Basics_ chapter contains a _Basic Usage_ section. [Its _First Start_ subsection](https://copyq.readthedocs.io/en/latest/basic-usage.html#first-start) starts with:

> To start CopyQ, double-click the program icon or run command `copyq`. This starts the graphical interface which can be accessed from the tray (NOTE: on OS X the tray defaults to the top-right of the screen and is not to be confused with Launchpad).

This will be at least confusing to users of Microsoft Windows, since on that OS, the command needed would have to use an absolute or relative path, and refer to the `CopyQ.exe` binary. Moreover, at least on Windows, no desktop icon is created by default.

The situation appears to be the same when installing using AppImage.

A more typical way to start CopyQ would be to launch it from the Start menu. However, I believe CopyQ 13 is launched by default, so this may not be necessary.

[The README's _Using the App_ section](https://github.com/hluk/CopyQ/blob/master/README.md#using-the-app) has the same issue.

By the way
OS X is now called "macOS".

[🅭🄍](https://www.philippecloutier.com/Common+infrastructure+licensing#its)