Adding in some git branch pictures

Author: bbrydsoe

docs/branches.md

@@ -33,18 +33,6 @@ Minor modifications done for the fall 2021/2022/2023 versions of the course. -->
 
 ## What is a Git branch?
 
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 * A pointer to a commit (ref: named pointer)
 * Defined as all points reachable in the commit graph from the named commit (the "tip" of the branch)
 * The ref HEAD determines what branch you are on. 
@@ -53,12 +41,8 @@ Minor modifications done for the fall 2021/2022/2023 versions of the course. -->
 
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 ## Why use branches?
 
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 There are many uses for branches:
 
 - Test different directions for a project
@@ -67,38 +51,26 @@ There are many uses for branches:
 
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 ## What is a Git branch?
 
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 Until now, we have worked with a repository that only have one branch, with the commits done one at a time: 
 
-![](https://i.imgur.com/OjpgqBz.png)
+![Git branch](../images/git-branch.png)
 
 In the above picture, the master branch points to a commit. The current position is HEAD. (Time goes rightwards)
 
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 ### What is a Git branch - basic concepts
 
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 Now we want to look at repositories with several branches: 
 
-![](https://i.imgur.com/9lvwmg9.png)
+![Git several branches](../images/git-several-branches.png)
 
 Branches are used to create another line of development.  They are "individual projects" within a git repository.
 
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 * The branch is the commit and all its parent commits, not just the one we are currently pointing at. 
 * The main line of development is usually called the "master" branch.
 * Different branches within a repository can have