docs: Fix invalid references and broken links

This commit fixes quite a few broken links and references, minor typos,
and improves wording in some sections.

docs/reference/gio/content-types.md

@@ -0,0 +1,15 @@
+Title: Content Types
+SPDX-License-Identifier: LGPL-2.1-or-later
+SPDX-FileCopyrightText: 2006, 2007 Red Hat, Inc.
+SPDX-FileCopyrightText: 2007 Alexander Larsson
+
+# Content Types
+
+A content type is a platform specific string that defines the type of a file.
+On UNIX it is a [MIME type](http://www.wikipedia.org/wiki/Internet_media_type)
+like `text/plain` or `image/png`.
+On Win32 it is an extension string like `.doc`, `.txt` or a perceived
+string like `audio`. Such strings can be looked up in the registry at
+`HKEY_CLASSES_ROOT`.
+On macOS it is a [Uniform Type Identifier](https://en.wikipedia.org/wiki/Uniform_Type_Identifier)
+such as `com.apple.application`.

docs/reference/gio/gio.toml.in

@@ -66,6 +66,8 @@ content_files = [
   "migrating-posix.md",
 
   "io-scheduler.md",
+
+  "content-types.md",
 ]
 content_images = [
   "gvfs-overview.png",
@@ -107,4 +109,4 @@ hidden = true
 
 [[function]]
 pattern = "win32_.+"
-hidden = true
+hidden = true

docs/reference/gio/meson.build

@@ -66,6 +66,7 @@ if get_option('documentation') and enable_gir
     'overview.md',
     'pollable-utils.md',
     'tls-overview.md',
+    'content-types.md',
   ]
   expand_content_unix_files = [
     'unix-mounts.md',