The subject line of a commit should explain what files or topic in the project is being modified as well as the overall change that is being made.
For example, if the overall documentation format is being changed to meet a new standard, a good subject line would be as follows:
documentation: rework to fit standard X
Another example, if a specific documentation file is being changed to fix spelling errors, a good subject line would be as follows:
documentation/some-file.md: fix spelling errors
The subject line should be no longer than 72 characters. Past this it will wrap when reading via a standard sized terminal. If the changes cannot be summarized in that length then the commit is likely better split into multiple commits.
The topic: summary of what changed format is preferred but will not be
enforced. As long as it includes the topic and a summary of what changed it is
acceptable.
The body of the commit should explain the why the commit is needed or wanted.
The body may also give more detail on what is being changed or how it is being changed.
With simple and obvious commits this is not always necessary and the body of the commit may be omitted.
Body text should usually not go past 72 characters per line. This is not a hard rule and can be broken where appropriate. For example, if error text is included in the commit body and is longer than 72 characters, it does not need to be broken into shorter lines.