Add Creating Non-Existent Directories as a vim til.

vim/creating-non-existent-directories.md

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+# Creating Non-Existent Directories
+
+When creating new files from withing vim, using `:e`, you may find yourself
+creating that file in a directory that doesn't yet exist. Vim will tell you
+as much if you then try to save that file. To get around this, I have often
+shelled out with `:!mkdir %:h`. This is a bit awkward to type though.
+
+The [`vim-eunuch`](https://github.com/tpope/vim-eunuch) plugin comes with a
+handy command for this. `:Mkdir` will create the parent directory for the
+current buffer. If you're in a situation where multiple levels of the
+buffer's directory don't exist, you can use `:Mkdir!` which will invoke
+`mkdir` with the `-p` flag.