patch 8.2.0563: Vim9: cannot split a function line

Problem:    Vim9: cannot split a function line.
Solution:   Continue in next line so long as the function isn't done.
diff --git a/runtime/doc/vim9.txt b/runtime/doc/vim9.txt
index 1d7aec9..88c35de 100644
--- a/runtime/doc/vim9.txt
+++ b/runtime/doc/vim9.txt
@@ -210,6 +210,13 @@
 Note that "enddef" cannot be used at the start of a continuation line, it ends
 the current function.
 
+It is also possible to split a function header over multiple lines, in between
+arguments: >
+	def MyFunc(
+		text: string,
+		separator = '-'
+		): string
+
 
 No curly braces expansion ~