Add bootstrap.dat to the download page

Mention short instructions about how to use bootstrap.dat
Add a warning icon and title to grab attention to the text

img/warning.svg

@@ -0,0 +1,73 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="42"
+   height="42"
+   id="svg2"
+   version="1.1"
+   inkscape:version="0.48.4 r9939"
+   sodipodi:docname="warning.svg"
+   inkscape:export-filename="/media/X/bitcoin.org/current/img/warning.png"
+   inkscape:export-xdpi="90"
+   inkscape:export-ydpi="90">
+  <defs
+     id="defs4" />
+  <sodipodi:namedview
+     id="base"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageopacity="0.0"
+     inkscape:pageshadow="2"
+     inkscape:zoom="11.2"
+     inkscape:cx="15.368938"
+     inkscape:cy="18.322975"
+     inkscape:document-units="px"
+     inkscape:current-layer="layer1"
+     showgrid="false"
+     inkscape:window-width="1680"
+     inkscape:window-height="1026"
+     inkscape:window-x="0"
+     inkscape:window-y="24"
+     inkscape:window-maximized="1" />
+  <metadata
+     id="metadata7">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <g
+     inkscape:label="Calque 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(0,-1010.3622)">
+    <path
+       style="fill:#ee9209;fill-opacity:1;stroke:#ee9209;stroke-width:8.95062447;stroke-linecap:round;stroke-linejoin:round;stroke-miterlimit:4;stroke-opacity:1;stroke-dasharray:none"
+       d="m 20.94413,1019.5343 -14.5466989,23.8635 29.1515569,0 z"
+       id="path2985"
+       inkscape:connector-curvature="0"
+       sodipodi:nodetypes="cccc" />
+    <g
+       style="font-size:28.56415749px;font-style:normal;font-variant:normal;font-weight:500;font-stretch:normal;line-height:125%;letter-spacing:0px;word-spacing:0px;fill:#ffffff;fill-opacity:1;stroke:none;font-family:Ubuntu;-inkscape-font-specification:Ubuntu Medium"
+       id="text3755">
+      <path
+         d="m 23.025738,1029.1502 c -6e-6,1.5805 -0.05713,3.0278 -0.171385,4.3417 -0.114262,1.314 -0.257083,2.6375 -0.428462,3.9704 l -2.456518,0 c -0.19043,-1.3329 -0.342772,-2.6564 -0.457026,-3.9704 -0.114259,-1.333 -0.171388,-2.7802 -0.171385,-4.3417 l 0,-5.313 3.684776,0 0,5.313 m 0.428463,12.5968 c -7e-6,0.6665 -0.218999,1.2092 -0.656976,1.6281 -0.437989,0.419 -0.980708,0.6284 -1.628157,0.6284 -0.628415,0 -1.171134,-0.2094 -1.628157,-0.6284 -0.437986,-0.4189 -0.656978,-0.9616 -0.656976,-1.6281 -2e-6,-0.6665 0.21899,-1.2092 0.656976,-1.6282 0.457023,-0.438 0.999742,-0.657 1.628157,-0.657 0.647449,0 1.190168,0.219 1.628157,0.657 0.437977,0.419 0.656969,0.9617 0.656976,1.6282"
+         style=""
+         id="path3779" />
+    </g>
+  </g>
+</svg>