Fix long option format on docs.podman.io

Escape the two dashes, otherwise they are combined into one long dash.
I tested that this change is safe and still renders correctly on github
and with the man pages.

This commit also contains a small change to make it build locally.
Assuming you have the dependencies installed you can do:
```
cd docs
make html
```
Preview the html files in docs/build/html with
`python -m http.server 8000 --directory build/html`.

Fixes containers/podman.io#373

Signed-off-by: Paul Holzinger <paul.holzinger@web.de>

1 files changed, 2 insertions, 2 deletions

diff --git a/docs/source/markdown/podman-diff.1.md b/docs/source/markdown/podman-diff.1.md
index dbab2d4db..5a4132783 100644
--- a/docs/source/markdown/podman-diff.1.md
+++ b/docs/source/markdown/podman-diff.1.md
@@ -13,11 +13,11 @@ Displays changes on a container or image's filesystem.  The container or image w
 
 ## OPTIONS
 
-#### **--format**
+#### **\-\-format**
 
 Alter the output into a different format.  The only valid format for diff is `json`.
 
-#### **--latest**, **-l**
+#### **\-\-latest**, **-l**
 
 Instead of providing the container name or ID, use the last created container. If you use methods other than Podman
 to run containers such as CRI-O, the last started container could be from either of those methods. (This option is not available with the remote Podman client)