docs: add description

cli/upgrade.go

@@ -17,6 +17,15 @@ var releaseCandidateURL = "https://git.coopcloud.tech/coop-cloud/abra/raw/branch
 var UpgradeCommand = &cli.Command{
 	Name:  "upgrade",
 	Usage: "Upgrade abra",
+	Description: `
+This command allows you to upgrade Abra in-place with the latest stable or
+release candidate.
+
+If you would like to install the latest release candidate, please pass the
+"--rc" option. Please bear in mind that the latest release candidate may have
+some catastrophic bugs contained in it. In any case, thank you very much for
+testing efforts!
+`,
 	Flags: []cli.Flag{internal.RCFlag},
 	Action: func(c *cli.Context) error {
 		cmd := exec.Command("bash", "-c", fmt.Sprintf("curl -s %s | bash", mainURL))