Build options missing in the documentation

[felix-schwarz]

mdm_tables.adoc also contains auto-generated documentation on available build flags that are available for branding. At the moment, this part of the documentation is not publicly visible and therefore inaccessible.

A new appendix should be added, covering the available build options for use in the Branding.plist file:

# Build options

== Introduction

The following build options are available for configuring custom builds via the `Branding.plist` file: 

include::./mdm_tables.adoc[tag=build]

If this should not be part of the documentation, I'd like to bring back doc/BUILD_CUSTOMIZATION.md to the owncloud/ios-app repository in its entirety to cover the gaps in documentation.

[michaelstingl]

If this should not be part of the documentation,

Everything should be visible. Was just never added. I can check later.