doc: convert git-checkout manpage to new style

- Switch the synopsis to a synopsis block which will automatically
  format placeholders in italics and keywords in monospace
- Use _<placeholder>_ instead of <placeholder> in the description
- Use `backticks` for keywords and more complex option
descriptions. The new rendering engine will apply synopsis rules to
these spans.

Signed-off-by: Jean-Noël Avila <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: jnavila

Documentation/config/checkout.adoc

@@ -1,9 +1,9 @@
-checkout.defaultRemote::
+`checkout.defaultRemote`::
 	When you run `git checkout <something>`
 	or `git switch <something>` and only have one
 	remote, it may implicitly fall back on checking out and
 	tracking e.g. `origin/<something>`. This stops working as soon
-	as you have more than one remote with a `<something>`
+	as you have more than one remote with a _<something>_
 	reference. This setting allows for setting the name of a
 	preferred remote that should always win when it comes to
 	disambiguation. The typical use-case is to set this to
@@ -12,31 +12,31 @@ checkout.defaultRemote::
 Currently this is used by linkgit:git-switch[1] and
 linkgit:git-checkout[1] when `git checkout <something>`
 or `git switch <something>`
-will checkout the `<something>` branch on another remote,
+will checkout the _<something>_ branch on another remote,
 and by linkgit:git-worktree[1] when `git worktree add` refers to a
 remote branch. This setting might be used for other checkout-like
 commands or functionality in the future.
 
-checkout.guess::
+`checkout.guess`::
 	Provides the default value for the `--guess` or `--no-guess`
 	option in `git checkout` and `git switch`. See
 	linkgit:git-switch[1] and linkgit:git-checkout[1].
 
-checkout.workers::
+`checkout.workers`::
 	The number of parallel workers to use when updating the working tree.
 	The default is one, i.e. sequential execution. If set to a value less
 	than one, Git will use as many workers as the number of logical cores
 	available. This setting and `checkout.thresholdForParallelism` affect
 	all commands that perform checkout. E.g. checkout, clone, reset,
 	sparse-checkout, etc.
 +
-Note: Parallel checkout usually delivers better performance for repositories
+NOTE: Parallel checkout usually delivers better performance for repositories
 located on SSDs or over NFS. For repositories on spinning disks and/or machines
 with a small number of cores, the default sequential checkout often performs
 better. The size and compression level of a repository might also influence how
 well the parallel version performs.
 
-checkout.thresholdForParallelism::
+`checkout.thresholdForParallelism`::
 	When running parallel checkout with a small number of files, the cost
 	of subprocess spawning and inter-process communication might outweigh
 	the parallelization gains. This setting allows you to define the minimum