Update README.md
Create CFEngine Concept Guide category and organize documents
Merge remote-tracking branch 'upstream/master'
Modified meta data for markdown files in bundles-logs-functions-variables to remove hyphens from all 'Categories' sections. Edited Bundles-for-agent-0-methods-in-agent-promises.markdown up to '### `create`' - mainly merging all 'Synopsis' and 'Notes' sections into a 'Description' section, an adjusting the text accordingly.