Add "key=value" placeholder to text tag editor textarea

data/core.yaml

@@ -557,6 +557,7 @@ en:
     edit_reference: "edit/translate"
     wiki_reference: View documentation
     wiki_en_reference: View documentation in English
+    key_value: "key=value"
     multiple_values: Multiple Values
     hidden_preset:
       manual: "{features} are hidden. Enable them in the Map Data pane."

modules/ui/raw_tag_editor.js

@@ -139,6 +139,7 @@ export function uiRawTagEditor(context) {
             .append('textarea')
             .attr('class', 'tag-text' + (_tagView !== 'text' ? ' hide' : ''))
             .call(utilNoAuto)
+            .attr('placeholder', t('inspector.key_value'))
             .attr('spellcheck', 'false')
             .merge(textarea);