Documentation files should have license notices also. Manuals should use the GNU Free Documentation License. Following is an example of the license notice to use after the copyright line(s) using all the features of the GFDL.

    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3 or
    any later version published by the Free Software Foundation; with the
    Invariant Sections being ``GNU General Public License'', with the
    Front-Cover Texts being ``A GNU Manual'', and with the Back-Cover Texts
    as in (a) below.  A copy of the license is included in the section
    entitled ``GNU Free Documentation License''.

    (a) The FSF's Back-Cover Text is: ``You have the freedom to
    copy and modify this GNU manual.  Buying copies from the FSF
    supports it in developing GNU and promoting software freedom.''

If the FSF does not publish this manual on paper, then omit the last sentence in (a) that talks about copies from GNU Press. If the FSF is not the copyright holder, then replace ‘`FSF`’ with the appropriate name.