From The Document Foundation Wiki
- if there is a bugreport related to the commit, it's mandatory to start the first line with a bug reference like tdf#12345 (see details below)
- use the rest of the first line as a concise summary of your changes. The maximum length for this line is 72 characters.
- use present tense. tell what the change does. be terse. avoid "decorations" like dashes and brackets that waste space.
- if you want to provide more text than what fits the 1st line, it's mandatory to leave the 2nd line empty
- starting from the 3rd line explain what the patch does and why, and if it not obvious also how. These lines should have 80 characters length at most; split into several lines, if your comment is longer. Here you can also describe how the code used to work incorrectly before the change.