[geary] Add F6 navigation shortcut keys to the help page.

[Adam Dingle <adamd src gnome org>]

commit d25b87f7a119a3c41a99cdda9ea8c92983d475f5
Author: Florin Lipan <florinlipan gmail com>
Date:   Mon Apr 11 20:55:28 2016 +0200

    Add F6 navigation shortcut keys to the help page.

 help/C/shortcuts.page |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/help/C/shortcuts.page b/help/C/shortcuts.page
index bcd085d..3530968 100644
--- a/help/C/shortcuts.page
+++ b/help/C/shortcuts.page
@@ -55,6 +55,10 @@
            <td><p>Mark unread</p></td>
                <td><p> <keyseq><key>Ctrl</key><key>U</key></keyseq> or 
<keyseq><key>Shift</key><key>U</key></keyseq> </p></td>
        </tr>
+    <tr>
+        <td><p>Move focus to the next/previous pane</p></td>
+      <td><p> <keyseq><key>F6</key></keyseq> / <keyseq><key>Shift</key><key>F6</key></keyseq> </p></td>
+    </tr>
        <tr>
            <td><p>Move focus to conversation list</p></td>
                <td><p> <keyseq><key>Ctrl</key><key>B</key></keyseq> </p></td>