Update README.rst

Update the README to elaborate on case-sensitivity in ignored words
and dictionaries.

Add an additional "Ignoring Words" section, with internal link from the
"noteworthy flags" overview.

Co-authored-by: Peter Newman <[email protected]>
Co-authored-by: Dimitri Papadopoulos Orfanos <[email protected]>

README.rst

@@ -55,25 +55,25 @@ Some noteworthy flags:
 
     codespell -w, --write-changes
 
-The ``-w`` flag will actually implement the changes recommended by codespell. Running without the ``-w`` flag is the same as with doing a dry run. It is recommended to run this with the ``-i`` or ``--interactive`` flag.
+The ``-w`` flag will actually implement the changes recommended by codespell. Running without the ``-w`` flag is the same as doing a dry run. It is recommended to run this with the ``-i`` or ``--interactive`` flag.
 
 .. code-block:: sh
 
     codespell -I FILE, --ignore-words=FILE
 
-The ``-I`` flag can be used for a list of certain words to allow that are in the codespell dictionaries. The format of the file is one word per line. Invoke using: ``codespell -I path/to/file.txt`` to execute codespell referencing said list of allowed words. **Important note:** The list passed to ``-I`` is case-sensitive based on how it is listed in the codespell dictionaries.
+The ``-I`` flag can be used for a list of certain words to allow that are in the codespell dictionaries. The format of the file is one word per line. Invoke using: ``codespell -I path/to/file.txt`` to execute codespell referencing said list of allowed words. See `Ignoring Words`_ for more details.
 
 .. code-block:: sh
 
     codespell -L word1,word2,word3,word4
 
-The ``-L`` flag can be used to allow certain words that are comma-separated placed immediately after it.  **Important note:** The list passed to ``-L`` is case-sensitive based on how it is listed in the codespell dictionaries.
+The ``-L`` flag can be used to allow certain words that are comma-separated placed immediately after it.  See `Ignoring Words`_ for more details.
 
 .. code-block:: sh
 
     codespell -x FILE, --exclude-file=FILE
 
-Ignore whole lines that match those in ``FILE``.  The lines in ``FILE`` should match the to-be-excluded lines exactly.
+Ignore whole lines that match those in ``FILE``.  The lines in ``FILE`` should match the to-be-excluded lines exactly. ::
 
 .. code-block:: sh
 
@@ -116,6 +116,25 @@ Want to know if a word you're proposing exists in codespell already? It is possi
 
 You can select the optional dictionaries with the ``--builtin`` option.
 
+Ignoring Words
+--------------
+
+When ignoring false positives, note that spelling errors are *case-insensitive* but words to ignore are *case-sensitive*. For example, the dictionary entry ``wrod`` will also match the typo ``Wrod``, but to ignore it you must pass ``wrod``.
+
+The words to ignore can be passed in two ways:
+
+1. ``-I``: A file with a word per line to ignore:
+
+.. code-block:: sh
+
+    codespell -I FILE, --ignore-words=FILE
+
+2. ``-L``: A comma separated list of words to ignore on the command line:
+
+.. code-block:: sh
+
+    codespell -L word1,word2,word3,word4
+
 Using a config file
 -------------------