making proper api citation

paper/.latexmkrc

@@ -1,6 +1,7 @@
 $pdf_mode = 1;
 $pdflatex = 'pdflatex -synctex=1 -interaction=nonstopmode -file-line-error %O %S';
-$bibtex_use = 2;                       # run bibtex when needed
-$bibtex   = 'bibtex %O %B';
+$bibtex_use = 2;                       # run biber when biblatex .bcf changes
+# biber runs with cwd = -outdir (paper/build); .bib paths are relative to paper/src
+$biber    = 'biber --input-directory=../src %O %S';
 $pdf_previewer = 'zathura %O %S';
 $clean_ext = 'synctex.gz bbl bcf run.xml fls fdb_latexmk glg glo gls ist blg lof lot out toc';