scripts: Patch relative links for correct doc generation

In doc/help/index.asciidoc, we have links like this:
    * link:../quickstart{outfilesuffix}[Quick start guide]

That is correct in e.g. the GitHub file structure, as those files are
stored in e.g. doc/quickstart.asciidoc indeed.

It's *no* longer true when we view the built files via qute://help,
however: There, this turns into a flat file structure, with those pages
being at qute://help/index.html and qute://help/quickstart.html,
respectively.

It looks like QtWebEngine < 6.5 did just ignore the
<a href="../quicktart.html"> and pointed from qute://help/index.html to
qute://help/quickstart.html anyways, weirdly.

With QtWebEngine 6.5, however, this is now interpreted as a link
pointing to qute://quickstart.html instead, which is clearly wrong.

Until we have a less messy doc generation (probably as part of #345),
let's just patch the link to be correct.

See #7624

scripts/asciidoc2html.py

@@ -84,12 +84,15 @@ class AsciiDoc:
             dst = DOC_DIR / (src.stem + ".html")
             files.append((src, dst))
 
-        # patch image links to use local copy
         replacements = [
+            # patch image links to use local copy
             ("https://raw.githubusercontent.com/qutebrowser/qutebrowser/master/doc/img/cheatsheet-big.png",
              "qute://help/img/cheatsheet-big.png"),
             ("https://raw.githubusercontent.com/qutebrowser/qutebrowser/master/doc/img/cheatsheet-small.png",
-             "qute://help/img/cheatsheet-small.png")
+             "qute://help/img/cheatsheet-small.png"),
+
+            # patch relative links to work with qute://help flat structure
+            ("link:../", "link:"),
         ]
         asciidoc_args = ['-a', 'source-highlighter=pygments']