[i18n] Add a couple of explanatory comments for translators (#9878)

frontend/apps/filemanager/filemanagermenu.lua

@@ -688,6 +688,7 @@ To:
     })
     if Device:isKobo() and Device:canToggleChargingLED() then
         table.insert(self.menu_items.developer_options.sub_item_table, {
+            -- @translators This is a debug option to help determine cases when standby failed to initiate properly. PM = power management.
             text = _("Turn on the LED on PM entry failure"),
             checked_func = function()
                 return G_reader_settings:isTrue("pm_debug_entry_failure")

plugins/opds.koplugin/opdsbrowser.lua

@@ -595,6 +595,7 @@ function OPDSBrowser:showDownloads(item)
         if acquisition.count then
             stream_buttons = {
                 {
+                    -- @translators "Stream" here refers to being able to read documents from an OPDS server without downloading them completely, on a page by page basis.
                     text = _("Page stream") .. "\u{2B0C}", -- append LEFT RIGHT BLACK ARROW
                     callback = function()
                         OPDSPSE:streamPages(acquisition.href, acquisition.count, false, self.root_catalog_username, self.root_catalog_password)
@@ -602,6 +603,7 @@ function OPDSBrowser:showDownloads(item)
                     end,
                 },
                 {
+                    -- @translators "Stream" here refers to being able to read documents from an OPDS server without downloading them completely, on a page by page basis.
                     text = _("Stream from page") .. "\u{2B0C}", -- append LEFT RIGHT BLACK ARROW
                     callback = function()
                         OPDSPSE:streamPages(acquisition.href, acquisition.count, true, self.root_catalog_username, self.root_catalog_password)