[gimp] devel-docs: document new "Messages" performance-log parameter

[Ell <ell src gnome org>]

commit d7de0781aba73d2a08c6083e97fc2b49bd84af8d
Author: Ell <ell_se yahoo com>
Date:   Sun Aug 2 10:57:48 2020 +0300

    devel-docs: document new "Messages" performance-log parameter

 .../performance-logs/performance-log-parameters.png   | Bin 7000 -> 8187 bytes
 devel-docs/performance-logs/performance-logs.md       |   5 +++++
 2 files changed, 5 insertions(+)
---
diff --git a/devel-docs/performance-logs/performance-log-parameters.png 
b/devel-docs/performance-logs/performance-log-parameters.png
index 4ec2c8bb32..33a0ec26ab 100644
Binary files a/devel-docs/performance-logs/performance-log-parameters.png and 
b/devel-docs/performance-logs/performance-log-parameters.png differ
diff --git a/devel-docs/performance-logs/performance-logs.md b/devel-docs/performance-logs/performance-logs.md
index 99e0e59dce..86e07468bc 100644
--- a/devel-docs/performance-logs/performance-logs.md
+++ b/devel-docs/performance-logs/performance-logs.md
@@ -119,6 +119,11 @@ otherwise.
     Backtraces capture the code-paths taken while recording the log, and should
     normally be included.
 
+  - *Messages:*
+    Whether or not to include diagnostic messages in the log.
+    Diagnostic messages indicate errors and unexpected conditions, and should
+    normally be included.
+
   - *Progressive:*
     Whether or not to record a progressive log.