patch 8.2.4594: need to write script to a file to be able to source them

Problem:    Need to write script to a file to be able to source them.
Solution:   Make ":source" use lines from the current buffer. (Yegappan
            Lakshmanan et al., closes #9967)
diff --git a/runtime/doc/repeat.txt b/runtime/doc/repeat.txt
index ce88a10..a775af0 100644
--- a/runtime/doc/repeat.txt
+++ b/runtime/doc/repeat.txt
@@ -197,6 +197,12 @@
 :so[urce] {file}	Read Ex commands from {file}.  These are commands that
 			start with a ":".
 			Triggers the |SourcePre| autocommand.
+
+:[range]so[urce] 	Read Ex commands from the [range] of lines in the
+			current buffer.  When sourcing commands from the
+			current buffer, the same script-ID |<SID>| is used
+			even if the buffer is sourced multiple times.
+
 							*:source!*
 :so[urce]! {file}	Read Vim commands from {file}.  These are commands
 			that are executed from Normal mode, like you type