docs: prevent smartphones from being too smart (docbook)

Add HTML <meta> tag to not auto-create telephone number links on mobile browsers also in docbook processed documents.

Reference: https://github.com/networkupstools/nut/issues/78

XSL files source:
- https://github.com/asciidoc/asciidoc/blob/master/docbook-xsl/common.xsl
- https://github.com/asciidoc/asciidoc/blob/master/docbook-xsl/xhtml.xsl
- https://github.com/asciidoc/asciidoc/blob/master/docbook-xsl/chunked.xsl