-Add build_an_executable_jar_subhead to README.ftl.md
-Revise Summary per language for other summaries
-Revise SIDEBAR.md per language for other Related Resources
-Revise "Understanding" to "Concepts and Technologies" per others
-Avoid excessive italics in README.ftl.md Looks jarring.
-In Summary section, suggest adding a link to Related Resources
(SIDEBAR.md) so reader doesn't have to scroll all the way back up page.
You don't want to put links in Summary because it's redundant and
Summary is about summing up current guide.
-Make Related Resources a main head, edit intro.