Add content to git-github roadmap (#6554)

src/data/roadmaps/git-github/content/git-config@NMCWgzhhfUvFOMO5GbF_u.md

@@ -1 +1,12 @@
 # git config
+
+The `git config` command is a convenience function that is used to set Git configuration values on a global or local project level. These configuration levels correspond to .gitconfig text files. Executing `git config` will modify a configuration text file.
+
+The most basic use case for `git config` is to invoke it with a configuration name, which will display the set value at that name. Configuration names are dot delimited strings composed of a 'section' and a 'key' based on their hierarchy. For example: `user.email`
+
+Learn more from the following resources:
+
+- [@official@Git - git-config Documentation](https://git-scm.com/docs/git-config)
+- [@article@git config | Atlassian Git Tutorial](https://www.atlassian.com/git/tutorials/setting-up-a-repository/git-config)
+- [@article@Setting your username in Git](https://docs.github.com/en/get-started/getting-started-with-git/setting-your-username-in-git)
+- [@article@Git config commands | Git tutorial](https://nulab.com/learn/software-development/git-tutorial/git-commands-settings/git-config-commands/)

src/data/roadmaps/git-github/content/git-init@1iOkbO5juk2LO-WZHx_W6.md

@@ -1 +1,8 @@
 # git init
+
+The `git init` command creates a new Git repository. It can be used to convert an existing, unversioned project to a Git repository or initialize a new, empty repository. Most other Git commands are not available outside of an initialized repository, so this is usually the first command you'll run in a new project.
+
+Learn more from the following resources:
+
+- [@official@Git - git-init Documentation](https://git-scm.com/docs/git-init)
+- [@article@git init | Atlassian Git Tutorial](https://www.atlassian.com/git/tutorials/setting-up-a-repository/git-init#:~:text=The%20git%20init%20command%20creates,run%20in%20a%20new%20project.)

src/data/roadmaps/git-github/content/gitignore@oz2oRAhaEQb0Fm3aRJQG8.md

@@ -1 +1,9 @@
 # .gitignore
+
+Ignored files are tracked in a special file named `.gitignore` that is checked in at the root of your repository. There is no explicit git ignore command: instead the `.gitignore` file must be edited and committed by hand when you have new files that you wish to ignore. `.gitignore` files contain patterns that are matched against file names in your repository to determine whether or not they should be ignored.
+
+Learn more from the following resources:
+
+- [@official@gitignore Documentation](https://git-scm.com/docs/gitignore/en)
+- [@article@.gitignore file - ignoring files in Git | Atlassian Git Tutorial](https://www.atlassian.com/git/tutorials/saving-changes/gitignore)
+- [@article@Ignoring files - GitHub Docs](https://docs.github.com/en/get-started/getting-started-with-git/ignoring-files)