Diagnostics instructions need updating

[gtnewton]

The instructions are no longer quite right (using Oxygen 22).
Following instructions for running in Oxygen:

• The Oxygen File/Open Project menu has been replaced with Project/Open Project
• Because the file doesn't actually open you can't press the transform button, and the Document menu is not available.
  Instead, right click the 'diagnostics.xpr' list heading (the one with the folder icon in the 'Project' panel on the left)
  and select 'Transform/Apply Transformation Scenario(s)'. Then the Oxygen directory selector pops up.
• Once running, the error mentioned below leaves the transformation running interminably although I do get a
  diagnostics browser window.

Running in CLI:

• Might be a problem with my XML, but I get the following error
  [java] Error at char 24 in xsl:value-of/@select on line 1020 column 173 of diagnostics_master.xsl:
  [java] FORX0003: The regular expression must not be one that matches a zero-length string
  [java] The regular expression must not be one that matches a zero-length string

• Following the 'BUILD SUCCESSFUL' message I get the following error
  [711692:711692:1216/133229.904147:ERROR:sandbox_linux.cc(374)] InitializeSandbox() called with multiple threads in process gpu-process.

• Probably nothing, but
  [open] Warning: Nashorn engine is planned to be removed from a future JDK release

Missing instructions(?)

• The resulting diagnostics page has two sections: 'Statistics' and 'Consistency Checks'. I get nothing in the 'Consistency Checks'
  section and there is no mention of this section in the instructions or README.md.

[martindholmes]

Fixed the documentation error, but the whole process fails for me in Oxygen 23 due to:

getDirectory:
Java 15 has removed Nashorn, you must provide an engine for running JavaScript yourself. GraalVM JavaScript currently is the preferred option.

This has been a threat for a while, and I guess it's finally bitten us. It might be necessary to just instruct people to run at the command line. It will affect other projects, though; any build file in which we depend on embedded JavaScript may well fail now in Oxygen; ultimately they'll probably fail at the command line too. This project is probably a good test case for working around these changes.

[martindholmes]

Added issue #23 to cover the Nashorn/JS issues; I'll close this one. If you get nothing in the consistency checks, then be happy -- it didn't find any bad internal links or similar issues.