fix(build): Disable sphinx manpage section dirs

Before sphinx 4.0, this was the default but was changed in 4.0.
Now by default the folder structure looks like this:

man
├── 1
│   └── polybar.1
└── 5
    └── polybar.5

This restores the old behavior where there weren't individual folders
for the different sections.

Fixes #2424
Ref: https://www.sphinx-doc.org/en/master/changes.html#id14

CHANGELOG.md

@@ -9,6 +9,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Build
+- Support building documentation on sphinx 4.0 ([`#2424`](https://github.com/polybar/polybar/issues/2424))
+
 ## [3.5.5] - 2021-03-01
 ### Build
 - Support older python sphinx versions again ([`#2356`](https://github.com/polybar/polybar/issues/2356))

doc/conf.py

@@ -185,6 +185,9 @@ man_pages = [
     ('man/polybar.5', 'polybar', 'configuration file for polybar(1)', [], 5)
 ]
 
+man_make_section_directory = False
+
+
 # -- Options for Texinfo output ----------------------------------------------
 
 # Grouping the document tree into Texinfo files. List of tuples