Extend documentation on argument files:

- handling of UTF8 encoded argument files
- limitation for quoted argument values

docs/index.adoc

@@ -1021,6 +1021,10 @@ For example, it is possible to have a path with a space,
 such as `c:\Program Files` that can be specified as either `"c:\\Program Files"` or,
 to avoid an escape, `c:\Program" "Files`.
 
+CAUTION: Argument files do have a limitation: parameter or option values enclosed in quotes must not be preceded by an equal sign.
+Something like `myoption="foo bar"` does *not* work inside an argument file.
+To work around this, either omit the equal sign (`myoption "foo bar"`) or enclose the whole expression in quotes (`"myoption=\"foo bar\""`).
+
 Lines starting with `#` are comments and are ignored.
 The comment character can be configured with `CommandLine.setAtFileCommentChar(Character)`,
 and comments can be switched off by setting the comment character to `null`.
@@ -1049,6 +1053,19 @@ The above will be expanded to the contents of the file:
 java MyCommand ABC -option=123 "X Y Z"
 ----
 
+CAUTION: Handling of UTF-8 encoded argument files is tricky on Windows OS.
+Either use `-DFile.encoding=UTF8` as VM argument or set the environment variable `JAVA_TOOL_OPTIONS`.
+So both command calls given below will work on a Windows command line:
+[source,cmd]
+----
+java -DFile.encoding=UTF8 MyCommand ABC -option=123 "X Y Z"
+----
+[source,cmd]
+----
+SET JAVA_TOOL_OPTIONS=-Dfile.encoding=UTF8
+java MyCommand ABC -option=123 "X Y Z"
+----
+
 
 @-file expansion can be switched off by calling `CommandLine::setExpandAtFiles` with `false`.
 If turned on, you can still pass a real parameter with an initial '@' character by escaping it