first pass at some docs for this idea

docs/metadata.md

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+# Gitignore Metadata
+
+This document outlines the additional metadata that can be associated with a gitignore template, and how tools can consume this metadata.
+
+## Metadata Location
+
+To add additional metadata to a gitignore template, add a new file to the same directory, with the matching name but ending in `yml`.
+
+For example:
+ - for `C.gitignore` the associated metadata will be stored in `C.yml`
+ - for `Global/JetBrains.gitignore` the metadata file will be `Global/JetBrains.gitignore`
+
+## Supported Fields
+
+The structure of these files is still being settled upon, but for the moment these are some proposed entries.
+
+#### `aliases`
+
+Some templates can be used to represent a number of different situations, and rather than duplicating files on disk and needing to keep these in sync, we can store a list of these entries as metadata.
+
+For example, JetBrains has a unified gitignore template that can be applied to all of their IDEs. Previously these were stored as comments in the header:
+
+```
+# Covers JetBrains IDEs: IntelliJ, RubyMine, PhpStorm, AppCode, PyCharm, CLion, Android Studio and WebStorm
+```
+
+These values can be represented as metadata, so that tools consuming this repository can use these entries as matches if the user is searching for a specific product:
+
+```yaml
+aliases:
+  - IntelliJ
+  - RubyMine
+  - PhpStorm
+  - AppCode
+  - PyCharm
+  - CLion
+  - Android Studio
+  - WebStorm
+  - Rider
+```
+
+#### `editors`
+
+There are a number of editors out there that support working with different languages. Rather than baking every editor's rules in every language that is supported, a list of additional templates that might be of interest
+
+```yaml
+editors:
+  - Global/JetBrains.gitignore
+  - Global/VisualStudioCode.gitignore
+```
+
+#### `reference`
+
+Some ecosystems have up-to-date documentation about things that are necessary to exclude from version control. To associate this with a template, this could be stored as a key-value pair in metadata:
+
+```yaml
+reference: https://intellij-support.jetbrains.com/hc/en-us/articles/206544839
+```