[mix-messy-graph] Add README

Author: woojiahao

mix_messy_graph/README.md

@@ -1,18 +1,20 @@
 # mix-messy-graph
 
-<!--- Insert exercise description -->
+You are writing user documentation for a product. You have already written documentation for a few new features, each in a separate branch. After merging the `feature-search` branch, you realise this way of merging can result in a complicated revision graph. Instead, you wish to merge these changes in a way that results in a simple linear revision graph.
 
 ## Task
 
-<!--- Insert exercise task, simplify what needs to be done -->
+1. Undo the merging of `feature-search`.
+2. Squash-merge the `feature-search` branch onto the `main` branch. Delete the `feature-search` branch.
+3. Similarly, squash-merge and delete the `feature-delete` branch, while resolving any merge conflicts -- in the `features.md`, the delete feature should appear after the search feature. 
+4. The `list` branch is not needed, as you have decided not to have that feature. Delete that branch.
 
-## Hints
+The resulting revision graph should be as follows:
 
-<!--- Insert hints here -->
-<!---
-    Use Github Markdown's collapsible content:
-    <details>
-    <summary>...</summary>
-    ...
-    </details>
--->
+```mermaid
+gitGraph BT:
+  commit id: "Add features.md"
+  commit id: "Mention feature for creating books" tag: "v10"
+  commit id: "Add the delete feature"
+  commit id: "Add the search feature"
+```