Add institute variable in template for title slide (#122)

contribute to #87 by bringing at least same template as in Pandoc
diff --git a/NEWS.md b/NEWS.md
index 0f88025..d34a036 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -6,7 +6,10 @@
 
 - Add `title-slide` id on the auto generated title slide to ease the styling using CSS.
 
-- Support `background-image` pandoc's variable as other slide framework to customize the option `parallaxBackgroundImage`. This duplicates the variable `parallaxBackgroundImage` which still get precedence.
+- Support more Pandoc's variable in `revealjs_presentation()` as documented in Pandoc for HTML slides:
+* `background-image` to customize the option `parallaxBackgroundImage`. This duplicates the variable `parallaxBackgroundImage` which still get precedence.
+* `institute` to provide another line in title slide between author and date
+* `toc-title` to provide a Title above the toc when `toc = TRUE`
 
 - Fix template to add the necessary CSS to format [columns layout](https://pandoc.org/MANUAL.html#columns) and other Pandoc's features (thanks, @atusy, #82).
 
diff --git a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
index 9729ed4..6253783 100644
--- a/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
+++ b/inst/rmarkdown/templates/revealjs_presentation/resources/default.html
@@ -542,6 +542,9 @@
 $for(author)$
     <h2 class="author">$author$</h2>
 $endfor$
+$for(institute)$
+    <h3 class="institute">$institute$</h2>
+$endfor$
 $if(date)$
     <h3 class="date">$date$</h3>
 $endif$