[clang-tidy] Fix documentation in modernize-avoid-c-style-cast (#171413)

Related discussion:
#171058 (comment)

Author: zeyi2

clang-tools-extra/docs/clang-tidy/checks/google/readability-casting.rst

@@ -10,3 +10,5 @@ for more information.
 Finds usages of C-style casts.
 
 https://google.github.io/styleguide/cppguide.html#Casting
+
+Corresponding cpplint.py check name: `readability/casting`.

clang-tools-extra/docs/clang-tidy/checks/modernize/avoid-c-style-cast.rst

@@ -3,6 +3,7 @@
 modernize-avoid-c-style-cast
 ============================
 
+Finds usages of C-style casts.
 
 C-style casts can perform a variety of different conversions (``const_cast``,
 ``static_cast``, ``reinterpret_cast``, or a combination). This makes them