Update references to "Git reference" (#16968)

Author: phil-blain

.gitattributes

@@ -2,5 +2,5 @@
 * text=auto
 # Explicitly declare text files we want to always be normalized and converted
 # to native line endings on checkout.
-*.md text
+*.md text diff=markdown
 *.json.br filter=lfs diff=lfs merge=lfs -text

content/get-started/quickstart/git-and-github-learning-resources.md

@@ -18,7 +18,7 @@ shortTitle: Learning resources
 ---
 ## Using Git
 
-Familiarize yourself with Git by visiting the [official Git project site](https://git-scm.com) and reading the [ProGit book](http://git-scm.com/book). You can review the [Git command list](https://git-scm.com/docs) or [Git command lookup reference](http://gitref.org) while using the [Try Git](https://try.github.com) simulator.
+Familiarize yourself with Git by visiting the [official Git project site](https://git-scm.com) and reading the [ProGit book](http://git-scm.com/book). You can also review the [Git command list](https://git-scm.com/docs).
 
 ## Using {% data variables.product.product_name %}