In case you want to improve the commit message with header and body after you created the commit, you can reword it. This approach is more useful because you know what the code does only after you wrote it.
git rebase -i origin/master
Then, your commits will appear:
pick e152ce2 Update framework
pick ffcf91e Some magic
pick fa672e1 Update comments
Select the commit you want to reword and save.
pick e152ce2 Update framework
reword ffcf91e Some magic
pick fa672e1 Update comments
Now, you have the opportunity to add header and body, where the first line will be the header.
Create perpetuum mobile
Redesign laws of physics with a pinch of imagination. Open a wormhole in 23 dimensions. Add protection to avoid high instability.