Added vim notes to the knowledge base

knowledge base/vim.md

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+# Vim
+
+## Tl;DR
+
+```shell
+# Get help on something.
+:help modeline
+```
+
+## Modelines
+
+Set different options for a particular file.
+
+> The `modeline` option must be enabled in order to take advantage of this.  
+> This option is **set** by default for Vim running in nocompatible mode, but some notable distributions of Vim disable it in the system's `vimrc` for security. In addition, the option is **off** by default when editing as `root`.
+
+See `:help modeline` for more information.
+
+The modeline line needs to:
+
+- be placed near the top of the file; how near, will depend on the modeline settings
+- start with a comment opening for the file type.
+
+> The space between the comment opening and 'vim' is necessary for the modeline to be recognized.
+
+Examples:
+
+```text
+# vim: set expandtab:
+
+# -*- mode: ruby -*-
+# vi: set ft=ruby :
+
+/* ex: set ts=8 sw=4 tw=0 noet : */
+```
+
+## Further readings
+
+- [Modeline magic]
+
+[modeline magic]: https://vim.fandom.com/wiki/Modeline_magic