swap symlink of README and includes/README

The GitHub Pages generator does not seem to like us having a
symlink in our _includes directory.

Author: peff

README.md

@@ -0,0 +1 @@
+_includes/README.md

README.md

@@ -0,0 +1,11 @@
+This homepage is maintained by editing files in the
+[git/git.github.io](https://github.com/git/git.github.io) repository on
+GitHub.
+
+It is meant to be edited collaboratively like a wiki, except that
+instead of a web form, you get to use a text editor and git. What could
+be better?
+
+If you want push access, contact [email protected] and provide your GitHub
+username. You may also send patches by mail (and feel free to cc
+[email protected] if appropriate).