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, 3 insertions, 3 deletions

diff --git a/docs/source/markdown/podman-unmount.1.md b/docs/source/markdown/podman-unmount.1.md
index 2832e5fdb..d09762d46 100644
--- a/docs/source/markdown/podman-unmount.1.md
+++ b/docs/source/markdown/podman-unmount.1.md
@@ -27,11 +27,11 @@ External containers are containers created in container/storage by other tools l
 Buildah and CRI-O.
 
 ## OPTIONS
-#### **--all**, **-a**
+#### **\-\-all**, **-a**
 
 All of the currently mounted containers will be unmounted.
 
-#### **--force**, **-f**
+#### **\-\-force**, **-f**
 
 Force the unmounting of specified containers' root file system, even if other
 processes have mounted it.
@@ -39,7 +39,7 @@ processes have mounted it.
 Note: This could cause other processes that are using the file system to fail,
 as the mount point could be removed without their knowledge.
 
-#### **--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