Document Open Media Vault WebDAV setup (#694)

* Create README.md

Create documentation on how to add WebDAV access to Open Media Vault and use it on Remotely Save

* Update README.md

Add link to Open Media Vault WebDAV documentation.

docs/remote_services/webdav_openmediavault/README.md

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+# Open Media Vault WebDAV
+
+## Link 
+https://www.openmediavault.org
+
+## Steps
+
+1. In Open Media Vault's UI, install the WebDAV plugin:
+   * System → Plugins → openmediavault-webdav
+2. Create a new Shared Folder
+   * Storage → Shared Folders → Create
+3. Enable WebDAV server
+   * Services → WedDAV → Enable → Select previously created Shared Folder
+4. Make sure Group is "webdav-users"
+5. Add {your username} to "webdav-users" group
+   * Users → Groups → webdav-users → Edit → Members
+6. Set folder permissions
+   * Storage → Shared Folders select the corresponding shared folder → Permissions → Set both {your username} and "webdav-users" group to "Read/Write" permissions
+7. Back to Shared Folders, set specific Access Control List permissions
+   * Select the shared folder → Access Control List → set {your username}, "webdav-users" and "www-data" to "Read/Write" permissions
+8. Install Remotely Save in Obsidian, select WebDAV, add the URL http://[your-server-ip]/webdav, use your user credentials and connect.