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

AX principle 2: comments show HOW with real values, not WHAT the type is.
The old comment restated the struct definition. Replaced with a concrete
construction example.

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

pkg/mining/xmrig.go

@@ -15,7 +15,9 @@ import (
 	"github.com/adrg/xdg"
 )
 
-// XMRigMiner represents an XMRig miner, embedding the BaseMiner for common functionality.
+// miner := &XMRigMiner{}
+// miner.Name = "xmrig"
+// miner.BinaryPath = "/usr/local/bin/xmrig"
 type XMRigMiner struct {
 	BaseMiner
 	FullStats *XMRigSummary `json:"-"` // Excluded from JSON to prevent race during marshaling