geometry: Adds a README

Signed-off-by: BlackMinou <romain.chanoir@viacesi.fr>

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+Basic geometry data structures and services.
+
+# Points and Lines
+
+The very basics of geometry needs, for two and three-dimensional space.
+
+# Boxes and detection collision
+
+Boxes module introduces Bounding boxes for Points and Lines and services to detect collision or inclusion between boxes.
+It means a simple and fast way to test collision but not really accurate since it uses bounding boxes.
+
+# Quadtrees
+
+A QuadTree is a tree data structure in which each internal node has exactly four children
+They're most often used to partition two-dimensional space by recursively subdividing
+it into four quadrants or regions.
+
+* They decompose space into adaptable cells
+* Each cell has a maximum capacity. When maximum is reached, the cell splits.
+
+Quadtrees are using Boxed objects to determine their distribution in the 2D space.
+
+This API provides two different types of Quadtree : Static and Dynamic (respectively `SQuadTree` and `DQuadTree`).
+
+* Static: When you create the QuadTree, you need to specify the region that it will cover
+
+* Dynamic: You just need to fill the quadtree with objects, and when the threshold is reached,
+it will automatically divide the current region, depending on the distribution of objects already in the region.
+
+# Polygons
+
+Some basic polygon services.
+
+This module contains interesting algorithms for `ConvexPolygon`only at the moment. A Convex polygon can be defined as follow :
+
+* All its interior angles are less than 180°. this means that all the vertices of the polygon
+will point outwards, away from the interior of the shape.
+
+* Every point on every line segment between two points inside or on the boundary of the polygon
+remains inside or on the boundary.
+
+* The polygon is entirely contained in a closed half-plane defined by each of its edges.
+
+* For each edge, the interior points are all on the same side of the line that the edge defines.
+
+* The angle at each vertex contains all other vertices in its edges and interior.
+
+A polygon which is not convex is called concave. Convex polygon are used because most
+geometric problems are simpler and faster on convex objects than on non-convex ones.
+
+Services provided :
+
+* Point in convex polygon
+* Intersection of convex polygon
+* Convex hull of a set of points
+* Triangulation of polygon