Add tooltips explaining multiplayer mod selection buttons

osu.Game/Localisation/MultiplayerMatchStrings.cs

@@ -24,6 +24,21 @@ namespace osu.Game.Localisation
         /// </summary>
         public static LocalisableString StartMatchWithCountdown(string humanReadableTime) => new TranslatableString(getKey(@"start_match_width_countdown"), @"Start match in {0}", humanReadableTime);
 
+        /// <summary>
+        /// "Choose the mods which all players should play with."
+        /// </summary>
+        public static LocalisableString RequiredModsButtonTooltip => new TranslatableString(getKey(@"required_mods_button_tooltip"), @"Choose the mods which all players should play with.");
+
+        /// <summary>
+        /// "Each player can choose their preferred mods from a selected list."
+        /// </summary>
+        public static LocalisableString FreeModsButtonTooltip => new TranslatableString(getKey(@"free_mods_button_tooltip"), @"Each player can choose their preferred mods from a selected list.");
+
+        /// <summary>
+        /// "Each player can choose their preferred difficulty, ruleset and mods."
+        /// </summary>
+        public static LocalisableString FreestyleButtonTooltip => new TranslatableString(getKey(@"freestyle_button_tooltip"), @"Each player can choose their preferred difficulty, ruleset and mods.");
+
         private static string getKey(string key) => $@"{prefix}:{key}";
     }
 }

osu.Game/Screens/OnlinePlay/FooterButtonFreeMods.cs

@@ -18,6 +18,7 @@ using osu.Game.Graphics.UserInterface;
 using osu.Game.Rulesets.Mods;
 using osu.Game.Screens.Select;
 using osuTK;
+using osu.Game.Localisation;
 
 namespace osu.Game.Screens.OnlinePlay
 {
@@ -95,6 +96,8 @@ namespace osu.Game.Screens.OnlinePlay
             SelectedColour = colours.Yellow;
             DeselectedColour = SelectedColour.Opacity(0.5f);
             Text = @"freemods";
+
+            TooltipText = MultiplayerMatchStrings.FreeModsButtonTooltip;
         }
 
         protected override void LoadComplete()

osu.Game/Screens/OnlinePlay/FooterButtonFreeStyle.cs

@@ -12,6 +12,7 @@ using osu.Framework.Graphics.UserInterface;
 using osu.Game.Graphics;
 using osu.Game.Graphics.Sprites;
 using osu.Game.Screens.Select;
+using osu.Game.Localisation;
 
 namespace osu.Game.Screens.OnlinePlay
 {
@@ -72,6 +73,8 @@ namespace osu.Game.Screens.OnlinePlay
             SelectedColour = colours.Yellow;
             DeselectedColour = SelectedColour.Opacity(0.5f);
             Text = @"freestyle";
+
+            TooltipText = MultiplayerMatchStrings.FreestyleButtonTooltip;
         }
 
         protected override void LoadComplete()

osu.Game/Screens/OnlinePlay/OnlinePlaySongSelect.cs

@@ -21,6 +21,7 @@ using osu.Game.Rulesets.Mods;
 using osu.Game.Screens.Select;
 using osu.Game.Users;
 using osu.Game.Utils;
+using osu.Game.Localisation;
 
 namespace osu.Game.Screens.OnlinePlay
 {
@@ -196,14 +197,16 @@ namespace osu.Game.Screens.OnlinePlay
             IsValidMod = IsValidMod
         };
 
-        protected override IEnumerable<(FooterButton, OverlayContainer?)> CreateSongSelectFooterButtons()
+        protected override IEnumerable<(FooterButton button, OverlayContainer? overlay)> CreateSongSelectFooterButtons()
         {
             var baseButtons = base.CreateSongSelectFooterButtons().ToList();
 
+            baseButtons.Single(i => i.button is FooterButtonMods).button.TooltipText = MultiplayerMatchStrings.RequiredModsButtonTooltip;
+
             freeModsFooterButton = new FooterButtonFreeMods(freeModSelect) { Current = FreeMods };
             var freeStyleButton = new FooterButtonFreeStyle { Current = FreeStyle };
 
-            baseButtons.InsertRange(baseButtons.FindIndex(b => b.Item1 is FooterButtonMods) + 1, new (FooterButton, OverlayContainer?)[]
+            baseButtons.InsertRange(baseButtons.FindIndex(b => b.button is FooterButtonMods) + 1, new (FooterButton, OverlayContainer?)[]
             {
                 (freeModsFooterButton, null),
                 (freeStyleButton, null)

osu.Game/Screens/OnlinePlay/OnlinePlayStyleSelect.cs

@@ -45,7 +45,7 @@ namespace osu.Game.Screens.OnlinePlay
 
         protected override FilterControl CreateFilterControl() => new DifficultySelectFilterControl(item);
 
-        protected override IEnumerable<(FooterButton, OverlayContainer?)> CreateSongSelectFooterButtons()
+        protected override IEnumerable<(FooterButton button, OverlayContainer? overlay)> CreateSongSelectFooterButtons()
         {
             // Required to create the drawable components.
             base.CreateSongSelectFooterButtons();

osu.Game/Screens/Select/SongSelect.cs

@@ -415,7 +415,7 @@ namespace osu.Game.Screens.Select
         /// Creates the buttons to be displayed in the footer.
         /// </summary>
         /// <returns>A set of <see cref="FooterButton"/> and an optional <see cref="OverlayContainer"/> which the button opens when pressed.</returns>
-        protected virtual IEnumerable<(FooterButton, OverlayContainer?)> CreateSongSelectFooterButtons() => new (FooterButton, OverlayContainer?)[]
+        protected virtual IEnumerable<(FooterButton button, OverlayContainer? overlay)> CreateSongSelectFooterButtons() => new (FooterButton, OverlayContainer?)[]
         {
             (ModsFooterButton = new FooterButtonMods { Current = Mods }, ModSelect),
             (new FooterButtonRandom