Fix use of "whitelist" in README

Use the recommended replacement "allowlist"

README.rst

@@ -41,11 +41,11 @@ The ``-w`` flag will actually implement the changes recommended by codespell. No
 
     codespell -I FILE, --ignore-words=FILE
 
-The ``-I`` flag can be used to whitelist certain words that are in the ``codespell_lib/data/dictionary.txt``. The format of the whitelist file is one word per line. Invoke using: ``codespell -I path/to/file.txt`` to execute codespell referencing said whitelist. **Important note:** The whitelist passed to ``-I`` is case-sensitive based on how it is listed in ``dictionary.txt``. ::
+The ``-I`` flag can be used to allowlist certain words that are in the ``codespell_lib/data/dictionary.txt``. The format of the allowlist file is one word per line. Invoke using: ``codespell -I path/to/file.txt`` to execute codespell referencing said allowlist. **Important note:** The allowlist passed to ``-I`` is case-sensitive based on how it is listed in ``dictionary.txt``. ::
 
     codespell -L word1,word2,word3,word4
 
-The ``-L`` flag can be used to whitelist certain words that are comma-separated placed immediately after it. ::
+The ``-L`` flag can be used to allowlist certain words that are comma-separated placed immediately after it. ::
 
     codespell -S, --skip=