writing: Consolidate into module

For now, contains bibtex and zathura options, though it will undoubtedly
increase as I add more writing utilities (such as jrnl) into the repo.

writing/README.md

@@ -1,6 +1,11 @@
-# Bibtex module
+# Writing module
 
 [bibtex](https://en.wikipedia.org/wiki/BibTeX) - plain-text reference management
+[zathura](git.pwmt.org) - keyboard-driven PDF reading
+
+This readme is a little out of date, as are the scripts below.
+They are old, I used them during my time as a student and they are probably written terribly.
+But I still think there is value in them, hence not removing them from the repo just yet.
 
 ## bib-due