add a logo and hints how to use it (and how not to use it)

I hope the logo is pitiful enough to motivate somebody with better design
skills to make a better one.

See also:

https://github.com/nsupdate-info/nsupdate.info/issues/78

logo/README

@@ -0,0 +1,22 @@
+The nsupdate.info logo(s) in this directory must ONLY be used
+
+relating to / referring to the software project "nsupdate.info"
+
+or
+
+relating to / referring to the dynamic dns service at http(s)://nsupdate.info
+
+
+Especially, you must NOT use the logo(s) for
+
+other software projects (including forks of nsupdate.info)
+
+or
+
+other services (including services running the nsupdate.info software or
+a fork of it).
+
+
+(this is just to avoid confusion - so if you mean / run / are something else,
+ then have a different logo, please)
+

logo/nsupdate.svg

@@ -0,0 +1,129 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   xmlns:osb="http://www.openswatchbook.org/uri/2009/osb"
+   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:xlink="http://www.w3.org/1999/xlink"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   width="240"
+   height="240"
+   id="svg2"
+   version="1.1"
+   inkscape:version="0.48.4 r9939"
+   sodipodi:docname="nsupdate.svg"
+   inkscape:export-filename="/home/tw/Desktop/nsupdate-240x240.png"
+   inkscape:export-xdpi="90"
+   inkscape:export-ydpi="90">
+  <defs
+     id="defs4">
+    <linearGradient
+       id="linearGradient5227">
+      <stop
+         style="stop-color:#f30000;stop-opacity:1;"
+         offset="0"
+         id="stop5229" />
+      <stop
+         style="stop-color:#000000;stop-opacity:0;"
+         offset="1"
+         id="stop5231" />
+    </linearGradient>
+    <linearGradient
+       id="linearGradient5217"
+       osb:paint="solid">
+      <stop
+         style="stop-color:#00ff00;stop-opacity:1;"
+         offset="0"
+         id="stop5219" />
+    </linearGradient>
+    <radialGradient
+       inkscape:collect="always"
+       xlink:href="#linearGradient5227"
+       id="radialGradient5203"
+       cx="120"
+       cy="932.36218"
+       fx="120"
+       fy="932.36218"
+       r="114.7539"
+       gradientTransform="matrix(1,0,0,1.0081515,0,-7.6001564)"
+       gradientUnits="userSpaceOnUse" />
+  </defs>
+  <sodipodi:namedview
+     id="base"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageopacity="0.0"
+     inkscape:pageshadow="2"
+     inkscape:zoom="3.7416667"
+     inkscape:cx="115.50216"
+     inkscape:cy="120"
+     inkscape:document-units="px"
+     inkscape:current-layer="layer1"
+     showgrid="false"
+     inkscape:window-width="1855"
+     inkscape:window-height="1056"
+     inkscape:window-x="65"
+     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="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(0,-812.36218)">
+    <rect
+       style="fill:#00f500;fill-rule:evenodd;stroke:url(#radialGradient5203);stroke-width:0.99700000000000000;stroke-linecap:butt;stroke-linejoin:miter;stroke-opacity:1;opacity:1;fill-opacity:1;stroke-miterlimit:4;stroke-dasharray:none"
+       id="rect2985"
+       width="228.51126"
+       height="230.3821"
+       x="5.7443695"
+       y="817.17114" />
+    <g
+       id="g5259"
+       transform="translate(0,25.943723)">
+      <text
+         sodipodi:linespacing="125%"
+         id="text5249"
+         y="856.46021"
+         x="25.615234"
+         style="font-size:40px;font-style:normal;font-weight:normal;line-height:125%;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;font-family:Sans"
+         xml:space="preserve"><tspan
+           y="856.46021"
+           x="25.615234"
+           id="tspan5251"
+           sodipodi:role="line">nsupdate</tspan><tspan
+           id="tspan5253"
+           y="906.46021"
+           x="25.615234"
+           sodipodi:role="line">.info</tspan></text>
+      <text
+         sodipodi:linespacing="125%"
+         id="text5255"
+         y="982.60718"
+         x="33.486328"
+         style="font-size:20px;font-style:normal;font-weight:normal;line-height:125%;letter-spacing:0px;word-spacing:0px;fill:#000000;fill-opacity:1;stroke:none;font-family:Sans"
+         xml:space="preserve"><tspan
+           y="982.60718"
+           x="33.486328"
+           id="tspan5257"
+           sodipodi:role="line">free dynamic dns</tspan></text>
+    </g>
+  </g>
+</svg>