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, 7 insertions, 7 deletions

diff --git a/docs/source/markdown/podman-volume-ls.1.md b/docs/source/markdown/podman-volume-ls.1.md
index 48853bdfd..5214980a3 100644
--- a/docs/source/markdown/podman-volume-ls.1.md
+++ b/docs/source/markdown/podman-volume-ls.1.md
@@ -8,25 +8,25 @@ podman\-volume\-ls - List all the available volumes
 
 ## DESCRIPTION
 
-Lists all the volumes that exist. The output can be filtered using the **--filter**
-flag and can be formatted to either JSON or a Go template using the **--format**
-flag. Use the **--quiet** flag to print only the volume names.
+Lists all the volumes that exist. The output can be filtered using the **\-\-filter**
+flag and can be formatted to either JSON or a Go template using the **\-\-format**
+flag. Use the **\-\-quiet** flag to print only the volume names.
 
 ## OPTIONS
 
-#### **--filter**=*filter*, **-f**
+#### **\-\-filter**=*filter*, **-f**
 
 Filter volume output.
 
-#### **--format**=*format*
+#### **\-\-format**=*format*
 
 Format volume output using Go template.
 
-#### **--help**
+#### **\-\-help**
 
 Print usage statement.
 
-#### **--quiet**, **-q**
+#### **\-\-quiet**, **-q**
 
 Print volume output in quiet mode. Only print the volume names.