Document that pydoctor exit with code 2 on intersphinx inventory read failure

Author: tristanlatr

README.rst

@@ -76,7 +76,7 @@ in development
 * Hide sidebar element title when all items under it are private.
 * Allow suppressing the footer's buildtime altogether with option ``--buildtime=no``.
 * Add project version on each HTML page.
-* When an  intersphinx inventory file fails to read, do not print the whole stack trace by default. 
+* When an  intersphinx inventory file fails to read, exit with code 2 and do not print the whole stack trace by default. 
   The -v flag will log exceptions' tracebacks.
 
 pydoctor 25.10.1