Update welcome message for 26.3b1 (#360)

Author: zooba

src/manage/commands.py

@@ -40,9 +40,8 @@
 
 WELCOME = f"""!B!Python install manager was successfully updated to {__version__}.!W!
 
-Indexes can now be signed to provide tamper detection. When an index signature
-is found to be invalid, the operation will be aborted without modifying your system.
-See !B!{HELP_URL}#index-signatures!W! for more information.
+Additional shebang configuration is now available. Please see
+!B!{HELP_URL}#shebang-lines!W! for more information.
 """
 
 # The 'py help' or 'pymanager help' output is constructed by these default docs,