Add help shortcut for source migration (closes #3951)

(cherry picked from commit 56c19e57a9)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/browse/migration/sources/MigrationSourcesController.kt

app/src/main/java/eu/kanade/tachiyomi/ui/browse/migration/sources/MigrationSourcesController.kt

@@ -1,6 +1,9 @@
 package eu.kanade.tachiyomi.ui.browse.migration.sources
 
 import android.view.LayoutInflater
+import android.view.Menu
+import android.view.MenuInflater
+import android.view.MenuItem
 import android.view.View
 import android.view.ViewGroup
 import androidx.recyclerview.widget.LinearLayoutManager
@@ -16,6 +19,7 @@ import eu.kanade.tachiyomi.ui.browse.migration.advanced.design.PreMigrationContr
 import eu.kanade.tachiyomi.ui.browse.migration.manga.MigrationMangaController
 import eu.kanade.tachiyomi.util.lang.await
 import eu.kanade.tachiyomi.util.lang.launchUI
+import eu.kanade.tachiyomi.util.system.openInBrowser
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
 import rx.schedulers.Schedulers
@@ -31,6 +35,10 @@ class MigrationSourcesController :
 
     private var adapter: SourceAdapter? = null
 
+    init {
+        setHasOptionsMenu(true)
+    }
+
     override fun createPresenter(): MigrationSourcesPresenter {
         return MigrationSourcesPresenter()
     }
@@ -54,6 +62,17 @@ class MigrationSourcesController :
         super.onDestroyView(view)
     }
 
+    override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
+        inflater.inflate(R.menu.source_migration, menu)
+    }
+
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        when (item.itemId) {
+            R.id.action_source_migration_help -> activity?.openInBrowser(HELP_URL)
+        }
+        return super.onOptionsItemSelected(item)
+    }
+
     fun setSources(sourcesWithManga: List<SourceItem>) {
         adapter?.updateDataSet(sourcesWithManga)
     }
@@ -95,4 +114,8 @@ class MigrationSourcesController :
         }
     }
     // SY <--
+
+    companion object {
+        const val HELP_URL = "https://tachiyomi.org/help/guides/source-migration/"
+    }
 }