Log format description missing

[Laguna1989]

There is no description of the content of the ninja log file format . This should be added in two places:

• The manual
• As a comment line in the top of the log file itself (.ninja_log)

From what I can piece together from the code, I assume the log contains start and end times, a timestamp (not sure about the unit?), the path of the generated object file and a command hash.

Adding this information to the log itself as well as to the manual will help people with understanding how to parse the file