[master] Doc issue in file modules/ROOT/pages/updates-upgrades-rollbacks.adoc

[pierreprinetti]

Code snippets include the $ sign when they are copied by clicking on the "copy" icon on the top-right corner of the textbox.

For example, copy-pasting the first code snippet to the terminal directly would yield:

$ $ rpm-ostree upgrade

The $ sign should be visible in the code snippet textbox, but should not be selectable like the rest of the text when manually copying to the clipboard, and should not be included in the copied snippet when clicking on the icon (clipboard.svg). I suspect this can be achieved with a bit of clever CSS.