Add man page files in Markdown format

This allow us to edit man pages in a humane format.

doc/README.md

@@ -0,0 +1,20 @@
+qBittorent man pages
+===
+
+Our man pages are written in Markdown format (.md) and we use [Pandoc](https://pandoc.org/) to
+convert them to roff (the man page format).
+Refer to [Pandoc's Markdown](https://pandoc.org/MANUAL.html#pandocs-markdown) for info
+on that specific format.
+
+To build the man pages:
+```shell
+pandoc -s -f markdown -t man qbittorrent.1.md -o qbittorrent.1
+pandoc -s -f markdown -t man qbittorrent-nox.1.md -o qbittorrent-nox.1
+```
+
+There is also an online converter you can use if you have trouble installing a
+local one: [link](https://pandoc.org/try/?text=&from=markdown&to=man) \
+You'll need to be careful when you copy the output to file as some headers will be missing.
+Careful not to overwrite the existing leading headers or trim off the trailing headers.
+
+Remember to commit Markdown files (\*.md) and the generated man pages (\*.1 files) after editing!