Create Contributing.md

@topfunky #42768 
@mtodd #42766 
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Author: Gregg Juan Eduardo Palomo Herrera

Contributing.md

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+---
+title: Contributing to GitHub Docs documentation
+shortTitle: Contribute to GitHub Docs
+intro: 'Learn about how the {% data variables.product.prodname_docs %} team creates documentation and how you can contribute.'
+layout: product-landing
+versions:
+  feature: 'contributing'
+featuredLinks:
+  startHere:
+    - /contributing/writing-for-github-docs/best-practices-for-github-docs
+    - /contributing/style-guide-and-content-model/style-guide
+    - /contributing/style-guide-and-content-model/about-the-content-model
+    - /contributing/collaborating-on-github-docs/about-contributing-to-github-docs
+changelog:
+  label: docs
+children:
+  - /writing-for-github-docs
+  - /style-guide-and-content-model
+  - /collaborating-on-github-docs
+  - /setting-up-your-environment-to-work-on-github-docs
+---