[gimp-web] Add err message w/o UTF-8 in README

[Pat David <patdavid src gnome org>]

commit f55abe90bec3e7b07d518e5e7fab2c7179d9cd84
Author: Pat David <patdavid gmail com>
Date:   Sat Jul 17 14:18:55 2021 -0500

    Add err message w/o UTF-8 in README

 README.md | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/README.md b/README.md
index 3de572fc..3068af64 100644
--- a/README.md
+++ b/README.md
@@ -88,6 +88,11 @@ To de-activate, `deactivate`.
 #### Windows Environment Variables
 
 Due to Windows character encoding, you may see an error when trying to run pelican.
+We were seeing this error specifically:
+
+```
+CRITICAL: 'charmap' codec can't decode byte 0x8f in position 32396: character maps to <undefined>
+```
 
 You'll need to set Python to use UTF-8 character encodings by setting an Environment Variable `PYTHONUTF8` 
to the value `1`.