Update .github/INCIDENT_RESPONSE.md

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Author: aclark4life

.github/INCIDENT_RESPONSE.md

@@ -218,7 +218,7 @@ After the fix is released and the advisory is public:
 - Fixed version(s)
 - Nature of the vulnerability (without full exploit details if still fresh)
 - Credit to the reporter (with their consent)
-- Upgrade instructions (`pip install --upgrade Pillow`)
+- Upgrade instructions (`python3 -m pip install --upgrade Pillow`)
 
 ---