Add comment for SocketTimeout

src/constants.ts

@@ -19,4 +19,7 @@ export enum Events {
     PullRequest = "pull_request"
 }
 
+// Socket timeout in milliseconds during download.  If no traffic is received
+// over the socket during this period, the socket is destroyed and the download
+// is aborted.
 export const SocketTimeout = 5000;