internal/app: update doc comments

A lot of these comments are quite old and have not been updated to reflect changes.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/app/app_linux.go

@@ -3,6 +3,7 @@ package app
 import (
 	"context"
 	"fmt"
+	"log"
 	"sync"
 
 	"hakurei.app/hst"
@@ -22,6 +23,14 @@ func New(ctx context.Context, os sys.State) (App, error) {
 	return a, err
 }
 
+func MustNew(ctx context.Context, os sys.State) App {
+	a, err := New(ctx, os)
+	if err != nil {
+		log.Fatalf("cannot create app: %v", err)
+	}
+	return a
+}
+
 type app struct {
 	id  *stringPair[state.ID]
 	sys sys.State