explicitly list openssl as a dependency

It's not necessarily pulled in as a dependency of another package due to
some distributions splitting the executable from the libraries.

static/build.html

@@ -262,6 +262,7 @@
                         <li>freetype2 and any OpenType/TrueType font (such as DejaVu but anything works)
                             for OpenJDK despite it being a headless variant without GUI support</li>
                         <li>ncurses5 (provided by the source tree for some tools but not others)</li>
+                        <li>openssl</li>
                         <li>rsync</li>
                         <li>unzip</li>
                         <li>zip</li>