Add note on filter-branch

README

@@ -2,6 +2,11 @@ glip is a Git Library In PHP. It allows you to access bare git repositories
 from PHP scripts, even without having git installed. The project's homepage is
 located at <http://fimml.at/glip>.
 
+
 glip was formerly part of eWiki, a wiki software written in PHP using git as
 version control backend. You can get more information on eWiki from
 <http://fimml.at/ewiki>.
+
+glip was split off eWiki on May 31, 2009. An attempt was made to preserve
+commit history by using git filter-branch; this also means that commit
+messages before May 31, 2009 may seem weird (esp. wrt file names).