site: borrow os logos from haskell platform download page

site/download/HEADER.html

@@ -53,9 +53,9 @@ To build your own custom version of hledger, see
 
 <table id="platformdocs">
 	<tr>
-		<th>GNU/Linux (intel)</th>
+		<th><img src="../linux.png" /><br />GNU/Linux (intel)</th>
-		<th>Mac</th>
+		<th><img src="../mac.png" /><br />Mac</th>
-		<th>Windows</th>
+		<th><img src="../windows.png" /><br />Windows</th>
 	</tr>
 	<tr>
 		<td>

site/hakyll.hs

@@ -46,6 +46,9 @@ main = hakyllWithConfiguration cfg $ do
       ,"highslide/graphics/geckodimmer.png"
       ,"highslide/graphics/close.png"
       ,"highslide/graphics/closeX.png"
+      ,"linux.png"
+      ,"mac.png"
+      ,"windows.png"
       ,"sshot.png"
       ,"watchhours.png"
       ,"hledger-screen-1.png"