Put warning in autogenerated test files

[olexandr-konovalov]

Test files named weddergaNN.tst are generated automatically using examples extracted from the package manual. They should have a BIG WARNING telling not to edit them, but to edit the corresponding lines in the manual source.

[olexandr-konovalov]

Will now look like this:

# wedderga, chapter 3
#
# DO NOT EDIT THIS FILE - EDIT EXAMPLES IN THE SOURCE INSTEAD!
#
# This file has been autogenerated with GAP. It contains examples
# extracted from the documentation. Each example is preceded by the
# comment which points to the location of its source.
#
gap> START_TEST( "wedderga03.tst");