Added purpose of file

[robertlugg]

The first words I read were "arm_allinea_studio". This suggested that that is the topic of this document. Instead, add a very brief introduction to describe what this document is for. I've created some text that is OK but feel free to modify.

[samcmill]

Great point about missing a description of the document itself. This applies equally to the autogenerated primitives and misc_api documentation as well.

These files are auto generated from the code using pydocmd.

@robertlugg are you up for investigating how a static header can be added to dynamically generated documentation using pydocmd? The configuration file is pydocmd.yml at the top level of the repository.