patch 8.1.1147: desktop file translations are requiring manual updates

Problem:    Desktop file translations are requiring manual updates.
Solution:   Use the .po files for desktop file translations. (Christian
            Brabandt)
diff --git a/runtime/vim.desktop b/runtime/vim.desktop
index a908faa..8e03b32 100644
--- a/runtime/vim.desktop
+++ b/runtime/vim.desktop
@@ -1,11 +1,18 @@
+# The vim.desktop file is generated by src/po/Makefile, do NOT edit.
+# Edit the src/po/vim.desktop.in file instead.
 [Desktop Entry]
+# Translators: This is the Application Name used in the Vim desktop file
 Name=Vim
+# Translators: This is the Generic Application Name used in the Vim desktop file
 GenericName=Text Editor
+# Translators: This is the comment used in the Vim desktop file
+Comment=Edit text files
+# The translations should come from the po file. Leave them here for now, they will
+# be overwritten by the po file when generating the desktop.file.
 GenericName[da]=Teksteditor
 GenericName[de]=Texteditor
 GenericName[pl]=Edytor tekstu
 GenericName[is]=Ritvinnsluforrit
-Comment=Edit text files
 Comment[af]=Redigeer tekslêers
 Comment[am]=የጽሑፍ ፋይሎች ያስተካክሉ
 Comment[ar]=حرّر ملفات نصية
@@ -78,7 +85,9 @@
 Exec=vim %F
 Terminal=true
 Type=Application
+# Translators: Search terms to find this application. Do NOT change the semicolons! The list MUST also end with a semicolon!
 Keywords=Text;editor;
+# Translators: This is the Icon file name. Do NOT translate
 Icon=gvim
 Categories=Utility;TextEditor;
 StartupNotify=false