Add Configure Global gitignore File as a git til

git/configure-global-gitignore-file.md

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+# Configure Global gitignore File
+
+There are some files that you know you'll never want tracked by git. You don't
+even want them showing up as an option. For these files, it can be nice to
+specify them in a global `.gitignore` file. Then you don't need to specify them
+for each project.
+
+This can be configured in `~/.gitconfig` under the `core` settings as
+`excludesFile`.
+
+```
+[core]
+	excludesFile = ~/.gitignore
+```
+
+Then, create `~/.gitignore` (that's as good a place as any to put it).
+
+```
+# global .gitignore
+.DS_Store
+wip_notes.md
+```
+
+You'll now notice that for any git project, the files you listed won't be
+showing up in the untracked list.
+
+You can also add this to your `~/.gitconfig` with this one-line command.
+
+```bash
+$ git config --global core.excludesfile ~/.gitignore
+```
+
+See `man git-config` and search `core.excludesFile` for more details.