Reorganize pdf docs to remove them from the source folder.

See merge request gysela-developpers/gyselalibxx!419

--------------------------------------------

src/geometryXVx/rhs/collisions_inter.hpp

@@ -18,7 +18,7 @@
  * function of different species. It is solved using a explicit time 
  * integrator (RK2 for instance).
  * 
- * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/src/geometryXVx/rhs/doc/collisions_intra_inter.pdf). 
+ * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/doc/geometryXVx/collisions_intra_inter.pdf). 
  */
 class CollisionsInter : public IRightHandSide
 {

src/geometryXVx/rhs/collisions_intra.hpp

@@ -33,7 +33,7 @@
  * that needs to be resolved at each spatial position of the simulation box. Note that this linear 
  * system depends on the considered spatial position. 
  * 
- * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/src/geometryXVx/rhs/doc/collisions_intra_inter.pdf). 
+ * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/doc/geometryXVx/collisions_intra_inter.pdf).
  */
 class CollisionsIntra : public IRightHandSide
 {

src/geometryXVx/rhs/kinetic_source.hpp

@@ -26,7 +26,7 @@
  * and energy parameters are equal to one (usual case), the resulting velocity_shape 
  * is maxwellian. 
  * 
- * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/src/geometryXVx/rhs/doc/kinetic_source.pdf). 
+ * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/doc/geometryXVx/kinetic_source.pdf). 
  */
 class KineticSource : public IRightHandSide
 {

src/geometryXVx/rhs/krook_source_adaptive.hpp

@@ -19,7 +19,7 @@
  * - amplitude(electrons, x, t) = m_amplitude (density_ions(x,t) - m_density) / (density_electrons(x,t) - m_density)  
  * so that the operator conserves locally the charge. 
  * 
- * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/src/geometryXVx/rhs/doc/krook_source.pdf). 
+ * The complete description of the operator can be found in [rhs docs](https://github.com/gyselax/gyselalibxx/blob/main/doc/geometryXVx/krook_source.pdf). 
  */
 class KrookSourceAdaptive : public IRightHandSide
 {