Fix dependencies in makefile and add some documentation

Makefile

+#Name that you would like for your resulting pdf file, without extension
 PDFNAME = thesis
+#The program that you use for viewing pdf files
+PDFVIEWER = evince
+#Change name of this if you change the name of demothesis.tex, should be name of the main tex file
 TEXMAINFILE = demothesis.tex
+#Location of latexmk binary
 MKLATEX = latexmk
+#Options to latexmk, should need to be changed
 MKLATEXOPTS = -pdf -pdflatex="pdflatex -interaction=nonstopmode" -use-make -jobname=$(PDFNAME)
 
 all: $(PDFNAME).pdf
 
-$(PDFNAME).pdf: $(TEXMAINFILE)
+$(PDFNAME).pdf: $(TEXMAINFILE) *.tex
 	$(MKLATEX) $(MKLATEXOPTS) $<
 
 view: $(PDFNAME).pdf
-	evince $(PDFNAME).pdf &
+	$(PDFVIEWER) $(PDFNAME).pdf &
 
 clean:
 	$(MKLATEX) -CA