Add italic variant of _Source Code Pro_ (v1.058)

Necessary because /static/ayu-highlight.css makes .hljs-comment use italics

Author: Nemo157

static/SourceCodePro-It.ttf.woff

@@ -50,6 +50,14 @@
     font-weight: 600;
     src: url("SourceCodePro-Semibold.woff") format('woff');
 }
+@font-face {
+    font-family: 'Source Code Pro';
+    font-style: italic;
+    font-weight: 400;
+    /* Avoid using locally installed font because bad versions are in circulation:
+     * see https://github.com/rust-lang/rust/issues/24355 */
+    src: url("SourceCodePro-It.ttf.woff") format('woff');
+}
 
 html,
 input,