README.txt instructions for custom function are wrong

For the computing function, the documentation in the readme file is wrong or incomplete in a number of ways.

1) The first parameter to the function is not $entity_field. It is &$entity_field. If you don't pass by reference then your changes will not get saved, since $entity_field is an array.

2) The readme says only "Your function should set the appropriate values to $entity_field.". It does not in any way indicate what appropriate values are, or what the data structure is. In particular, it DOES need to contain a delta but should NOT contain a langcode. It took some experimentation to figure that out. The data structure needs to be properly documented.

Marking as major, as this is a serious gap in documentation and the first point is simply wrong.