Add Computer Modern font for later use

hdoc_to_pdf/font/README.md

+# Hdoc to PDF font selection
+
+The font used for PDF generation through FS is the **Computer Modern** font, the default LaTeX's one. Here are the main families to use :
+- `cmunrm.ttf` for default text ;
+- `cmunrd.ttf` for **bold** text ;
+- `cmunti.ttf` for *italic/emphasis* text ;
+- `cmuntt.ttf` for `code syntax`.