Add note about not being a general spell checking tool. (#1535)

Co-authored-by: Eric Larson <larson.eric.d@gmail.com>
Co-authored-by: Peter Newman <peternewman@users.noreply.github.com>
Co-authored-by: bl-ue <bl-ue@users.noreply.github.com>
diff --git a/.github/workflows/codespell-private.yml b/.github/workflows/codespell-private.yml
index 5231030..7b3f299 100644
--- a/.github/workflows/codespell-private.yml
+++ b/.github/workflows/codespell-private.yml
@@ -33,7 +33,7 @@
       - run: python setup.py install
       - run: codespell --help
       - run: make check
-      - run: codespell --check-filenames --skip="./.git/*,*.pyc,./codespell_lib/tests/test_basic.py,./codespell_lib/data/*,./example/code.c,./build/lib/codespell_lib/tests/test_basic.py,./build/lib/codespell_lib/data/*"
+      - run: codespell --check-filenames --skip="./.git/*,*.pyc,./codespell_lib/tests/test_basic.py,./codespell_lib/data/*,./example/code.c,./build/lib/codespell_lib/tests/test_basic.py,./build/lib/codespell_lib/data/*,README.rst,*.egg-info/*"
       # this file has an error
       - run: "! codespell codespell_lib/tests/test_basic.py"
       - run: codecov
diff --git a/.github/workflows/codespell.yml b/.github/workflows/codespell.yml
index 06229fb..e3a064a 100644
--- a/.github/workflows/codespell.yml
+++ b/.github/workflows/codespell.yml
@@ -13,4 +13,4 @@
         with:
           check_filenames: true
           # When using this Action in other repos, the --skip option below can be removed
-          skip: ./.git,./codespell_lib/data,./example/code.c,test_basic.py,*.pyc
+          skip: ./.git,./codespell_lib/data,./example/code.c,test_basic.py,*.pyc,README.rst
diff --git a/README.rst b/README.rst
index f4a586c..de9f4be 100644
--- a/README.rst
+++ b/README.rst
@@ -3,6 +3,10 @@
 
 Fix common misspellings in text files. It's designed primarily for checking
 misspelled words in source code, but it can be used with other files as well.
+It does not check for word membership in a complete dictionary, but instead
+looks for a set of common misspellings. Therefore it should catch errors like
+"adn", but it will not catch "adnasdfasdf". This also means it shouldn't
+generate false-positives when you use a niche term it doesn't know about.
 
 Useful links
 ------------