fix: package lane arrow assets

assets/lane-icons/upstream/DESIGN.md

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+## Design Guidelines
+
+The icons in this project follow closely the design guidelines established in the
+[MUTCD Standard Highway Signs guide](http://mutcd.fhwa.dot.gov/ser-shs_millennium.htm),
+2009 edition published by the US Federal Highway Administration.
+
+The MUTCD is [in the public domain](http://mutcd.fhwa.dot.gov/knowledge/faqs/faq_general.htm#printq5)
+and as such it is not copyrighted.
+
+Each icon should be
+
+* 25px x 25px
+* SVG
+* Single color fill
+* Path outline only, no stroke
+* Pixel grid aligned (where possible)
+
+### Arrows
+
+Arrows use the "Standard Arrow" described in MUTCD Standard Highway Signs
+[Appendix](http://mutcd.fhwa.dot.gov/ser-shs_millennium.htm).
+
+An upward facing Standard Arrow is included in this icon pack, and forms the basis of all turn
+lane arrows.
+
+<img alt='Standard Arrow' width='300px' src='docs/standard_arrow.png'/>
+
+
+Arrowhead rotation angles are chosen based on the turn lane indication:
+
+<table>
+<tr>
+    <th>Through</th>
+    <th>Slight Left</th>
+    <th>Left</th>
+    <th>Sharp Left</th>
+    <th>Reverse Left</th>
+</tr>
+<tr>
+    <td>no rotation<br/>
+        <img alt='Through' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/through.svg'/>
+    </td>
+    <td>45 degrees<br/>
+        <img alt='Slight Left' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/slight_left.svg'/>
+    </td>
+    <td>70 or 90 degrees<br/>
+        <img alt='Left' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/left.svg'/>
+    </td>
+    <td>135 degrees<br/>
+        <img alt='Sharp Left' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/sharp_left.svg'/>
+    </td>
+    <td>180 degrees<br/>
+        <img alt='Reverse Left' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/reverse_left.svg'/>
+    </td>
+</tr>
+</table>
+
+As the number of arrows increases, the arrows scale down:
+
+<table>
+<tr>
+    <th>1 Arrow</th>
+    <th>2 Arrows</th>
+    <th>3 Arrows</th>
+    <th>4 Arrows</th>
+</tr>
+<tr>
+    <td>
+        <ul><li>3px stroke</li><li>standard arrowhead</li></ul>
+        <img alt='Through' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/through.svg'/>
+    </td>
+    <td>
+        <ul><li>2.5px stroke</li><li>83% scaled arrowhead</li></ul>
+        <img alt='Left, Through' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/left-through.svg'/>
+    </td>
+    <td>
+        <ul><li>2.25px stroke</li><li>75% scaled arrowhead</li></ul>
+        <img alt='Left, Slight Left, Through' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/left-slight_left-through.svg'/>
+    </td>
+    <td>
+        <ul><li>2px stroke</li><li>66% scaled arrowhead</li></ul>
+        <img alt='Reverse Left, Left, Slight Left, Through' width='100px' src='https://cdn.rawgit.com/openstreetmap/lane-icons/master/docs/reverse_left-left-slight_left-through.svg'/>
+    </td>
+</tr>
+</table>
+
+
+Other important rules for arrows:
+* Bottom aligned with each other, 2px from icon bottom edge
+* Left-right centered
+* Smooth curves, no kinks
+* Arrow shaft path connects to the arrowhead anchor point
+
+
+### Other Icons
+
+Other non-arrow icons (bus, hov, pedestrian, tram, etc) also imitiate the icons found
+in the MUTCD Standard Highway Signs [Appendix](http://mutcd.fhwa.dot.gov/ser-shs_millennium.htm).