README: capitalize "documentation".
</p>
<p align = "center">
<strong>
- <a href="http://ncollide.org/rustdoc/ncollide2d">2D documentation</a> | <a href="http://ncollide.org/rustdoc/ncollide3d">3D documentation</a> | <a href="http://ncollide.org">User Guide</a> | <a href="http://users.nphysics.org">Forum</a>
+ <a href="http://ncollide.org/rustdoc/ncollide2d">2D Documentation</a> | <a href="http://ncollide.org/rustdoc/ncollide3d">3D Documentation</a> | <a href="http://ncollide.org">User Guide</a> | <a href="http://users.nphysics.org">Forum</a>
</strong>
</p>
