README: Confusing AppImage paragraph in Other Linux Distributions section

[The _Other Linux Distributions_ section of the `README`](https://github.com/hluk/CopyQ/blob/master/README.md#other-linux-distributions) starts with:
> Download the latest **AppImage** from [GitHub Releases](https://github.com/hluk/CopyQ/releases):
>
> ```bash
> chmod +x CopyQ-*.AppImage
> ./CopyQ-*.AppImage
> ```

Normally, a sequence of steps following a colon constitutes an algorithm which performs the action preceding the column. However, the sequence in this case launches CopyQ rather than downloading it, so the paragraph is confusing.

While a list of all steps would be ideal, replacing the colon with a period could constitute a minimal fix.

By the way
I am not sure this method should be listed first.

For one thing, it does not add `copyq` to `PATH`, making it impossible to follow documentation such as instructions in the `README` (see #3354).

Secondly, it does not add CopyQ to Kickoff (the "K menu").

Finally, it does not document how to uninstall.

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