appdata: nicely space out the nested tags

data/gnome-sudoku.appdata.xml.in

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Copyright 2013 Michael Catanzaro and contributors -->
 <application>
-<id type="desktop">gnome-sudoku.desktop</id>
-<licence>CC0</licence>
-<_name>GNOME Sudoku</_name>
-<description>
-<_p>
-GNOME Sudoku has a simple, unobstrusive interface with all the features that make playing Sudoku 
-fun. Games are automatically saved when you quit, and you can always come back to any game that
-you've played.
-</_p>
-<_p>
-Each game is assigned a difficulty similar to those given by newspapers and websites.
-You can also see detailed information about how the computer solved the puzzle.
-</_p>
-<_p>
-If you like to play on paper, you can print games out. You can choose how many games you want to
-print per page and what difficulty of games you want to print: as a result, GNOME Sudoku can act a
-renewable Sudoku book for you.
-</_p>
-</description>
-<screenshots>
-<_screenshot type="default" width="800" height="447">https://people.gnome.org/~mcatanzaro/gnome-sudoku.png</_screenshot>
-</screenshots>
-<url type="homepage">https://wiki.gnome.org/GnomeSudoku</url>
-<updatecontact>games-list_at_gnome.org</updatecontact>
+  <id type="desktop">gnome-sudoku.desktop</id>
+  <licence>CC0</licence>
+  <_name>GNOME Sudoku</_name>
+  <description>
+    <_p>
+      GNOME Sudoku has a simple, unobstrusive interface with all the features
+      that make playing Sudoku fun. Games are automatically saved when you quit,
+      and you can always come back to any game that you've played.
+    </_p>
+    <_p>
+      Each game is assigned a difficulty similar to those given by newspapers
+      and websites. You can also see detailed information about how the computer
+      solved the puzzle.
+    </_p>
+    <_p>
+      If you like to play on paper, you can print games out. You can choose how
+      many games you want to print per page and what difficulty of games you
+      want to print: as a result, GNOME Sudoku can act a renewable Sudoku book
+      for you.
+    </_p>
+  </description>
+  <screenshots>
+    <_screenshot type="default" width="800" height="447">https://people.gnome.org/~mcatanzaro/gnome-sudoku.png</_screenshot>
+  </screenshots>
+  <url type="homepage">https://wiki.gnome.org/GnomeSudoku</url>
+  <updatecontact>games-list_at_gnome.org</updatecontact>
 </application>