ax(mining): replace prose comment with usage example on InstallationDetails

AX Principle 2: comments that restate the type signature add zero
information. Replaced with a concrete call site showing how to
obtain and inspect the struct.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/mining.go

@@ -45,7 +45,8 @@ type Miner interface {
 	WriteStdin(input string) error
 }
 
-// InstallationDetails contains information about an installed miner.
+// details, err := miner.CheckInstallation()
+// if details.IsInstalled { fmt.Println(details.Version, details.Path) }
 type InstallationDetails struct {
 	IsInstalled bool   `json:"is_installed"`
 	Version     string `json:"version"`