public DocServiceBuilder include(DocServiceFilter filter) {
        requireNonNull(filter, "filter");
        if (includeFilter == ALL_SERVICES) {
            includeFilter = filter;
        } else {
            includeFilter = includeFilter.or(filter);
        }
        return this;
    }
Adds the {@link DocServiceFilter} that checks whether a method will be <b>included</b> while building
{@link DocService}. The {@link DocServiceFilter} will be invoked with the plugin, service and
method name. The rule is as follows:
<ul>
  <li>No {@link #include(DocServiceFilter)} and {@link #exclude(DocServiceFilter)} is called -
      include all methods.</li>
  <li>Only {@link #exclude(DocServiceFilter)} is called -
      include all methods except the methods which the exclusion filter returns {@code true}.</li>
  <li>Only {@link #include(DocServiceFilter)} is called -
      include the methods which the inclusion filter returns {@code true}.</li>
  <li>{@link #include(DocServiceFilter)} and {@link #exclude(DocServiceFilter)} is called -
      include the methods which the inclusion filter returns {@code true} and the exclusion filter
      returns {@code false}.</li>
</ul>

<P>Note that this can be called multiple times and the {@link DocServiceFilter}s are composed using
{@link DocServiceFilter#or(DocServiceFilter)} and {@link DocServiceFilter#and(DocServiceFilter)}.

@see #exclude(DocServiceFilter)
@see DocService to find out how DocService generates documentaion
core/src/main/java/com/linecorp/armeria/server/docs/DocServiceBuilder.java