feat: spellcheck input (#6446)

Reviewed-by: Mm2PL <mm2pl+gh@kotmisia.pl>
Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>
Reviewed-by: fourtf <tf.four@gmail.com>

src/widgets/settingspages/GeneralPage.cpp

@@ -481,6 +481,21 @@ void GeneralPage::initLayout(GeneralPageView &layout)
             "yours is successfully sent in the matching channel.")
         ->addTo(layout);
 
+#ifdef CHATTERINO_WITH_SPELLCHECK
+    SettingWidget::checkbox("Check spelling by default (experimental)",
+                            s.enableSpellChecking)
+        ->setTooltip(
+            u"Check the spelling of words in the input box of all splits by "
+            "default. This can be overwritten per split in the context menu."
+            " Chatterino does not include dictionaries - they have to "
+            "be downloaded or created manually. Chatterino expects Hunspell "
+            "dictionaries in '" %
+            getApp()->getPaths().dictionariesDirectory %
+            u"'. The file index.aff has to contain the affixes and index.dic "
+            u"must contain the dictionary (subject to change).")
+        ->addTo(layout);
+#endif
+
     layout.addTitle("Messages");
 
     SettingWidget::checkbox("Separate with lines", s.separateMessages)