Adding a note about commit messages.

This note will later be expanded into more information about commit
messages.
Adding an example commit message.

This can help people build a good practice about making commit messages
within the repository.
Adding a second file to the repository.

Here one can see what it looks like when a file is added to a
repository.
XuCommitTest

Add my user name and date
Merge origin/xuchongang/cosm2/new-branch

Merging after solving conflicts on Changelog