add note about IPv6-only accessibility

README.md

@@ -24,13 +24,14 @@ Here are two examples of generated diagrams (taken from the [Python grammar][PYT
 
 RR accepts grammars in [W3C-style EBNF][W3C-EBNF]. Some other representations, including
 some parser generator input notations, can be converted to W3C-style using
-[Grammar Conversion][CONVERT].
+the [ebnf-convert][CONVERT] Grammar Converter (note: IPv6-only). This tool
+is also available [on GitHub][CONVERT-GITHUB].
 
 # Distribution
 
 RR comes as a .zip, containing a .war file. The .war file can be deployed
 in servlet containers like Tomcat or Jetty for serving the GUI. This makes up the webapp
-that is running on the original website, <https://www.bottlecaps.de/rr/ui>.
+that is running on the original website, <https://www.bottlecaps.de/rr/ui> (note: IPv6-only).
 
 The .war file is a Java "executable war", i.e. it can also be started
 standalone from command line. Two different tasks can be performed in standalone mode:
@@ -77,12 +78,13 @@ RR is released under the [Apache 2 License][ASL].
 
 ## Links
 
-The official website for RR is <https://www.bottlecaps.de/rr/ui>.
+The official website for RR is <https://www.bottlecaps.de/rr/ui> (note: IPv6-only).
 
 [ASL]: http://www.apache.org/licenses/LICENSE-2.0
 [PYTHON]: https://docs.python.org/3/reference/grammar.html
 [W3C-EBNF]: http://www.w3.org/TR/2010/REC-xquery-20101214/#EBNFNotation
 [CONVERT]: http://www.bottlecaps.de/ebnf-convert/
+[CONVERT-GITHUB]: https://github.com/GuntherRademacher/ebnf-convert
 [SAXON]: http://www.saxonica.com/products/products.xml
 [TAGSOUP]: https://search.maven.org/artifact/org.ccil.cowan.tagsoup/tagsoup/1.2.1/jar
 [BATIK]: https://xmlgraphics.apache.org/batik/