Add documentation regarding pattern library and instance sheet
The current documentation on the pattern library is partly outdated. It is missing information like the fact that it is a Sketch library and the presence of a separate instance sheet.
- Create a consistent naming scheme for the symbols
- Create a separate instance sheet for common UI patterns
- Update the pattern library documentation to include getting started, workflow, plugins, etc.
- Remove the pages Global components and Page components from the pattern library sketch file (these will be available in the instance sheet)
- Remove the getting started page from the pattern library (this will be available in the pattern library documentation)