Add Case-Insensitive Substitution as a vim til.

README.md

@@ -147,6 +147,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Alternate Files With vim-rails](vim/alternate-files-with-vim-rails.md)
 - [The Black Hole Register](vim/the-black-hole-register.md)
 - [Buffer Time Travel](vim/buffer-time-travel.md)
+- [Case-Insensitive Substitution](vim/case-insensitive-substitution.md)
 - [Check Your Current Color Scheme](vim/check-your-current-color-scheme.md)
 - [Close the Current Buffer](vim/close-the-current-buffer.md)
 - [Coerce The Current Filetype](vim/coerce-the-current-filetype.md)

vim/case-insensitive-substitution.md

@@ -0,0 +1,18 @@
+# Case-Insensitive Substitution
+
+Use the `i` `s-flag` to perform a case-insensitive substitution (search and
+replace).
+
+For instance, `:%s/blog/article/gi` will turn
+
+```
+blog bLOg BLOG Blog
+```
+
+into
+
+```
+article article article article
+```
+
+See `:h s_flags` for more details.