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>

docs/source/markdown/podman-load.1.md

@@ -26,7 +26,7 @@ Note: `:` is a restricted character and cannot be part of the file name.
 
 ## OPTIONS
 
-#### **--input**, **-i**=*input*
+#### **\-\-input**, **-i**=*input*
 
 Read from archive file, default is STDIN.
 
@@ -34,11 +34,11 @@ The remote client requires the use of this option.
 
 NOTE: Use the environment variable `TMPDIR` to change the temporary storage location of container images. Podman defaults to use `/var/tmp`.
 
-#### **--quiet**, **-q**
+#### **\-\-quiet**, **-q**
 
 Suppress the progress output
 
-#### **--help**, **-h**
+#### **\-\-help**, **-h**
 
 Print usage statement