Clarify the status of the files in the documentation directory with respect to the manual

[ngirard]

The documentation folder has contents which can't be found in the Pandocomatic manual.
This leaves the newcomer unsure:

• about which one is the source of truth, between the manual and the documentation directory;
• whether reading the manual is enough to grasp Pandocomatic, or the files in documentation are also a required reading.

Thus, a clarification would be welcome.

[Huub de Beer]

The pandocomatic manual and the project's Github README.md file are generated from the files in the documentation folder and the contents should be the same. However, I do see there's a manual.md and a manual2.md, where the latter has superseded the former. I'll overwrite the former with the contents of the latter, after which I'll remove manual2.md. This should resolve this issue.