Rename exercises dir

Name it instead "topics" so it won't be
strange if some topics included "exercises" directory.

topics/git/commit_01.md

@@ -0,0 +1,20 @@
+## Git Commit 01
+
+### Objective
+
+Learn how to commit changes in Git repositories
+
+### Instructions
+
+1. Create a new directory
+2. Make it a git repository
+3. Create a new file called `file` with the content "hello commit"
+4. Commit your new file
+5. Run a git command to verify your commit was recorded
+
+### After you complete the exercise
+
+Answer the following:
+
+* What are the benefits of commits?
+* Is there another way to verify a commit was created?