Add Release note (using new-notes scheme from PR #628)

documentation/new-notes/PR-644.md

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+### Expand the use of colour in the IOCs output
+
+This release includes various changes to iocsh.cpp and elsewhere to add and
+expand the use of color:
+
+- When loading a startup script, the IOC Shell now displays comment lines in
+blue, and uses bold to make command lines stand out from other text.
+
+- The `softIoc -v` output also uses the above color scheme for the commands it
+prints.
+
+- The default IOC Shell prompt is now displayed in green; this color can be
+modified in the `configure/CONFIG_SITE_ENV` file for all targets, or set for
+a specific target by adding a `configure/os/CONFIG_SITE_ENV.<arch>` file.
+The value of the `IOCSH_PS1` environment paremeter in those files can use the
+`ANSI_ENV_*` and `ANSI_*()` color macros found in errlog.h to configure the
+appearance of the prompt. The C string literal concatenation syntax can be
+used to construct the prompt string:
+
+    IOCSH_PS1 = ANSI_ESC_RED "e" ANSI_ESC_YELLOW "p" ANSI_ESC_GREEN "i" ANSI_ESC_CYAN "c" ANSI_BLUE("s") "> "
+
+- More error messages printed by IOC Shell commands now appear in red, or use
+the red `ERROR` prefix that was introduced in previous releases.
+
+- The word "Illegal" has been replaced with "Invalid" in several Shell error
+messages.
+
+- The iocsh `var` command now shows the data type of the registered variables
+as well as their values.