Installation instructions should specify to rename the unzipped plugin directory

[trevorthornton]

After unzipping the plugin, the unzipped directory needs to be renamed from as_spreadsheet_bulk_updater-1.0 to as_spreadsheet_bulk_updater. This isn't mentioned in the installation instructions but it won't work without it.

[payten]

Thanks @trevorthornton, have added an extra instruction.