macos: Document ctrl-space global shortcut conflict (#23239)

assets/keymaps/default-macos.json

@@ -414,6 +414,8 @@
       "cmd-k cmd-9": ["editor::FoldAtLevel", { "level": 9 }],
       "cmd-k cmd-0": "editor::FoldAll",
       "cmd-k cmd-j": "editor::UnfoldAll",
+      // Using `ctrl-space` in Zed requires disabling the macOS global shortcut.
+      // System Preferences->Keyboard->Keyboard Shortcuts->Input Sources->Select the previous input source (uncheck)
       "ctrl-space": "editor::ShowCompletions",
       "cmd-.": "editor::ToggleCodeActions",
       "cmd-k r": "editor::RevealInFileManager",