documentation: add xsltproc, DocBook XSL, po4a

See #1865.

NEWS.md

@@ -1,3 +1,19 @@
+# Version ?
+
+## Build system changes
+
+* Up to and including release 9.8.0 the man pages and their translations came
+  pre-built and bundled with the source code. Those pre-built files have now
+  been removed and must be built during the build process. Therefore the tool
+  "xsltproc" and the DocBook XSL stylesheets for man pages are now required
+  dependencies. Additionally the tool "po4a" must be installed for the
+  translated man pages to be built and installed, though this is optional.
+
+  In order to facilitate finding the new requirements new options have been
+  added to confiure: "--with-xsltproc=prog", "--with-docbook-xsl=dir",
+  "--with-po4a=prog" and "--with-po4a-translate=prog.
+
+
 # Version 9.8.0 "Kuglblids" 2017-01-22
 
 ## Important notes

README.md

@@ -92,6 +92,10 @@ programs and libraries you absolutely need are:
   used: "format", "RegEx", "filesystem", "system", "math",
   "Range", "rational", "variant". At least v1.46.0 is required.
 
+- [libxslt's xsltproc binary](http://xmlsoft.org/libxslt/) and
+  [DocBook XSL stylesheets](https://sourceforge.net/projects/docbook/files/docbook-xsl/)
+  — for creating man pages from XML documents
+
 You also need the `rake` or `drake` build program. I suggest `rake`
 v10.0.0 or newer (this is included with Ruby 2.1) as it offers
 parallel builds out of the box. If you only have an earlier version of
@@ -118,6 +122,9 @@ built. These include:
 - [libMagic](http://www.darwinsys.com/file/) from the "file" package
   for automatic content type detection
 
+- [po4a](https://po4a.alioth.debian.org/) for building the translated
+  man pages
+
 ## 2.3. Building libEBML and libMatroska
 
 This is optional as MKVToolNix comes with its own set of the