manual, news: Document org-html-meta-tags

* docs/org-manual.org, etc/ORG-NEWS: Document and announce the new
setting `org-html-meta-tags'.

[km: spacing and spelling tweaks]

doc/org-manual.org

@@ -12624,6 +12624,9 @@ settings described in [[*Export Settings]].
   multiple =DESCRIPTION= lines.  The exporter takes care of wrapping
   the lines properly.
 
+  The exporter includes a number of other meta tags, which can be customized
+  by modifying ~org-html-meta-tags~.
+
 - =HTML_DOCTYPE= ::
 
   #+cindex: @samp{HTML_DOCTYPE}, keyword

etc/ORG-NEWS

@@ -81,6 +81,13 @@ block. ~org-babel-latex-preamble~, ~org-babel-latex-begin-env~ and
 the user to specify the preamble and code that preceedes and proceeds
 the contents of the source block.
 
+*** New option ~org-html-meta-tags~ allows for HTML meta tags customization
+
+New variable ~org-html-meta-tags~ makes it possible to customize the
+=<meta>= tags used in an HTML export.  Accepts either a static list of
+values, or a function that generates such a list (see
+~org-html-meta-tags-default~ as an example of the latter).
+
 ** New features
 *** =ob-python= improvements to =:return= header argument