Python: Highlight os.path.join behavior with absolute paths

Author: RasmusWL

python/ql/src/Security/CWE-022/PathInjection.qhelp

@@ -43,7 +43,8 @@ In the second example, it appears that the user is restricted to opening a file
 special characters. For example, the string <code>"../../../etc/passwd"</code> will result in the code
 reading the file located at <code>"/server/static/images/../../../etc/passwd"</code>, which is the system's
 password file. This file would then be sent back to the user, giving them access to all the
-system's passwords.
+system's passwords. Note that it is still possible to use an absolute path, since the result of
+<code>os.path.join("/server/static/images/", "/etc/passwd")</code> is <code>"/etc/passwd"</code>.
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