adding note on asciidoctor-mathematical limitations and output to svg…

… for math expressions in build command

README.md

@@ -259,7 +259,7 @@ This generates a file named `any_file_name.html`.
 For pdf output, cd into this cloned directory and use this command:
 
 ```cmd
-asciidoctor-pdf -r asciidoctor-diagram -r asciidoctor-mathematical -r asciidoctor-bibtex book_header.adoc -a pdf-style=resources/themes/risc-v_spec-pdf.yml -a pdf-fontsdir=resources/fonts
+asciidoctor-pdf -r asciidoctor-diagram -r asciidoctor-mathematical -a mathematical-format=svg -r asciidoctor-bibtex book_header.adoc -a pdf-style=resources/themes/risc-v_spec-pdf.yml -a pdf-fontsdir=resources/fonts
 ```
 
 This generates a file named `book_header.pdf` that makes use of the graphics, styles, and fonts that is identical to example.pdf. 

tables_graphics.adoc

@@ -496,7 +496,9 @@ NOTE: Asciidoctor supports dditional diagram types. For information on additiona
 
 === Mathematical notations
 
-While not all of the RISC-V specifications make use of mathematical notations, some make frequent use of superscipts and other mathematical notation..
+WARNING: Asciidoctor-mathematical has some limitations. For inline expressions, the graphical representations appear small and they are centered virtically. In some cases where there is a single character expresssion, they unintentionally look like superscripts. For this reason, we should attempt to use any viable alternatives like simple italics or unicode (see <<Unicode symbols>>).
+
+While not all of the RISC-V specifications make use of mathematical notations, some make frequent use of specific mathematical notation.
 
 To indicate a superscript, enclose the string for the superscript in carets as in the following example: