Improve reference docs for sphereTransform

[imagejan]

The API reference docs for sphereTransform (for all of Java, Matlab and Icy) currently don't make a lot of sense:

• the output is created with the same size as the input:
  

  clij2-docs/reference_sphereTransform.md

  Line 35 in c94f45d

  destination = clij2.create(input);

  
  and it's unclear how the correct output dimensions can be derived from a given input.
  I'd suggest to add something along the lines of the actual computation in clij{2,x}-assistant to the docs:
  https://github.com/clij/clij2-assistant/blob/1cef95e60735399c994c7e3186b1c2aa03059c5d/src/main/java/net/haesleinhuepf/clij2/assistant/interactive/handcrafted/SphereTransform.java#L83-L85
  https://github.com/clij/clijx-assistant/blob/6b6c719098179ee3fe6afa6317aba0b6d70d927a/src/main/java/net/haesleinhuepf/clijx/assistant/interactive/handcrafted/SphereTransform.java#L83-L85

• the center coordinates are arbitrarily set:
  

  clij2-docs/reference_sphereTransform.md

  Lines 38 to 40 in c94f45d

  	float relative_center_x = 2.0;
  	float relative_center_y = 3.0;
  	float relative_center_z = 4.0;

  
  If they are supposed to represent relative values as the name suggests, they should be between 0.0 and 1.0, or otherwise their name should be changed (see also SphereTransform: center coords are not relative clij2#42)