Update TDG, chapter Assemblies (missing association)

[tomschr]

Problem

Chapter "Assemblies", section "Relationships" contains a description about the relationship(s) structure.

The section shows this example:

<relationship type="seealso">
  <instance linkend="tut1"/>
  <instance linkend="tut2"/>
  <instance linkend="task1"/>
</relationship>

However, this example is a bit misleading as it seems to be incomplete. The section and the example has the following issues:

• Does not mention <relationships> (plural!) element
• Does not distinguish between <relationships> (plural) and <relationship> (singular)
• Does not mention <association> element as it required in DocBook 5.2*

Possible solution

IMHO, we should amend this example like this:

<relationships>
  <relationship type="seealso">
    <association>???</association>
    <instance linkend="tut1"/>
    <instance linkend="tut2"/>
    <instance linkend="task1"/>
  </relationship>
</relationship>

Not sure what we should put inside the <association> element.

Related issue

docbook/docbook#214