Symbols for index-modifying cards, remove index/mv level for now

Plus better descriptions for pull/push/fetch.

levels/unused/index-mv

@@ -0,0 +1,26 @@
+title = Rename a file in the next commit
+cards = add reset-file checkout-file mv commit
+
+[description]
+
+Other times, you might want to rename a file in the next commit. Use
+
+    git mv [file] [new name]
+
+for that. The effect is very similar as if you had created a copy with a new name, and removed the old version.
+
+[setup]
+
+echo a > a
+echo SPECIAL > b
+echo x > c
+git add .
+git commit -m "Initial commit"
+echo x > a
+echo b >> b
+git add b
+
+[win]
+
+# Make a commit where you rename the file b to "x".
+test "$(git ls-tree --name-only main)" = "$(echo -e "a\nc\nx")"