Restructure and move Git content (#18336)

* Rename map topic

* Delete map topic

* Rename map topic

* Add redirect

* Remove last two map topics

* Move article on adding a remote into a long-form guide

* Move article on changing a remote's URL

* Move articles on renaming and removing remotes

* Move remote URL article

* Fix typo

* Remove category index file

* Move a few articles to the new category

* Move a few more files

* Move managing remote repos article

* Move the rest of the getting started with git map topic

* Move the first half of the using git map topic

* Move the rest of the articles and 🔥 the directory

* Fix failing test

* Remove Using Git from product index

* Apply suggestions from code review

Co-authored-by: Laura Coursen <lecoursen@github.com>

* Apply suggestions from code review

Co-authored-by: Laura Coursen <lecoursen@github.com>

content/github/getting-started-with-github/dealing-with-non-fast-forward-errors.md

@@ -0,0 +1,39 @@
+---
+title: Dealing with non-fast-forward errors
+intro: 'Sometimes, Git can''t make your change to a remote repository without losing commits. When this happens, your push is refused.'
+redirect_from:
+  - /articles/dealing-with-non-fast-forward-errors
+  - /github/using-git/dealing-with-non-fast-forward-errors
+versions:
+  free-pro-team: '*'
+  enterprise-server: '*'
+  github-ae: '*'
+---
+
+If another person has pushed to the same branch as you, Git won't be able to push your changes:
+
+```shell
+$ git push origin main
+> To https://{% data variables.command_line.codeblock %}/<em>USERNAME</em>/<em>REPOSITORY</em>.git
+>  ! [rejected]        main -> main (non-fast-forward)
+> error: failed to push some refs to 'https://{% data variables.command_line.codeblock %}/<em>USERNAME</em>/<em>REPOSITORY</em>.git'
+> To prevent you from losing history, non-fast-forward updates were rejected
+> Merge the remote changes (e.g. 'git pull') before pushing again.  See the
+> 'Note about fast-forwards' section of 'git push --help' for details.
+```
+
+You can fix this by [fetching and merging](/github/getting-started-with-github/getting-changes-from-a-remote-repository) the changes made on the remote branch with the changes that you have made locally:
+
+```shell
+$ git fetch origin
+# Fetches updates made to an online repository
+$ git merge origin <em>YOUR_BRANCH_NAME</em>
+# Merges updates made online with your local work
+```
+
+Or, you can simply use `git pull` to perform both commands at once:
+
+```shell
+$ git pull origin <em>YOUR_BRANCH_NAME</em>
+# Grabs online updates and merges them with your local work
+```