Adjust documentation for Sphinx 4.0.

Discussed upstream at <https://github.com/ganeti/ganeti/pull/1615>.

diff --git a/doc/index.rst b/doc/index.rst
--- a/doc/index.rst
+++ b/doc/index.rst
@@ -119,7 +119,6 @@ Draft designs
    design-hotplug.rst
    design-internal-shutdown.rst
    design-kvmd.rst
-   design-location.rst
    design-linuxha.rst
    design-location.rst
    design-lu-generated-jobs.rst
diff --git a/lib/build/shell_example_lexer.py b/lib/build/shell_example_lexer.py
--- a/lib/build/shell_example_lexer.py
+++ b/lib/build/shell_example_lexer.py
@@ -79,4 +79,4 @@ class ShellExampleLexer(RegexLexer):
 
 
 def setup(app):
-  app.add_lexer("shell-example", ShellExampleLexer())
+  app.add_lexer("shell-example", ShellExampleLexer)
koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>refs</a><a class='active' href='/guix/log/tests/guix-describe.sh'>log</a><a href='/guix/tree/tests/guix-describe.sh?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>tree</a><a href='/guix/commit/tests/guix-describe.sh?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>commit</a><a href='/guix/diff/tests/guix-describe.sh?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/tests/guix-describe.sh'>
<input type='hidden' name='id' value='1edd63b699a3dc894a8e86ca56511ac776e1b519'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>root</a>/<a href='/guix/log/tests?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>tests</a>/<a href='/guix/log/tests/guix-describe.sh?id=1edd63b699a3dc894a8e86ca56511ac776e1b519'>guix-describe.sh</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/guix-describe.sh?id=1edd63b699a3dc894a8e86ca56511ac776e1b519&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-09-07 11:40:22 +0200'>2018-09-07</span></td><td><a href='/guix/commit/tests/guix-describe.sh?id=bd7470185bae15e686c2b2a83d3f61807e6fa527'>Add 'guix describe'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/describe.scm: New file.
* Makefile.am (MODULES): Add it.
(SH_TESTS): Add tests/guix-describe.sh.
* po/guix/POTFILES.in: Add it.
* guix/scripts/pull.scm (display-profile-content): Export.
* guix/describe.scm (current-profile, current-profile-entries): Export.
* tests/guix-describe.sh: New file.
* doc/guix.texi (Features): Mention 'guix pull' and provenance tracking.
(Invoking guix pull): Link to 'guix describe'.
(Channels): Likewise.
(Invoking guix describe): New node.
</span></span></td><td>Ludovic Courtès</td></tr>