Github Print Bookmarklet (like others, but does not require jQuery). Paste the minified javascript: into a bookmark to use it.

github-print-bookmarklet.js

/* Remove stuff from the page to make github pages pretty for printing */

console.log("Github pretty print 0.1");

function removeClassElems(name) {
    console.log("looking for class:", name);
    Array.from(document.getElementsByClassName(name)).forEach(function(e) {
        console.log("Removing", e);
        e.parentNode.removeChild(e);
    });
}

/* Classes to remove from DOM */
[
  "anchor",
  "header",
  "pagehead",
  "site-footer",
  "file-header",
  "file-navigation",
  "commit-tease",
  "all_commit_comments",
  "thread-subscription-status",
  "discussion-timeline",
].forEach(removeClassElems);

/* remove border */
Array.from(document.getElementsByClassName("file")).forEach(function(e) {
    console.log("Removing border from", e);
    e.style.border = "none";
});

github-print-bookmarklet.min.js

javascript:console.log("Github pretty print 0.1");function removeClassElems(name){console.log("looking for class:",name);Array.from(document.getElementsByClassName(name)).forEach(function(e){console.log("Removing",e);e.parentNode.removeChild(e)})}["anchor","header","pagehead","site-footer","file-header","file-navigation","commit-tease","all_commit_comments","thread-subscription-status","discussion-timeline",].forEach(removeClassElems);Array.from(document.getElementsByClassName("file")).forEach(function(e){console.log("Removing border from",e);e.style.border="none"})