Update index.rst

[nlyubova]

Add details about a mesh center

[vrabaud]

What does object center mean ? Center of gravity ? center of bounding box ?
Couldn't you center your object in your code automatically ?
In wg-perception/ork_tutorials#10, the mesh is only centered in 2d with respect to a bounding rectangle. Does that suffice ?

[nlyubova]

In the code, each object is centered to its origin, so the origin is supposed to be near the object's center (however, in any case ICP would align it afterwards).
Regarding meshes, all of meshes I use are centered to the centermass and it works quite well to align them during recognition , but you are right that better to center them based on the bounding box (and it is assume to be so when grasping an object)

based on that, no code changes are required, but each mesh should be centered to its bounding box. Do you agree?