Add some simpe readme with legal stuff, usage and some notes

Signed-off-by: Rocco Rutte <pdmef@gmx.net>

README.txt

@@ -0,0 +1,33 @@
+hg2git.(sh|py) - mercurial to git converter using git-fast-import
+
+Legal
+=====
+
+The scripts are licensed under the GPL version 2 and were written by
+Rocco Rutte <pdmef@gmx.net> with hints and help from the git list and
+#mercurial on freenode.
+
+Usage
+=====
+
+Using it is quite simple for a mercurial repository <repo>:
+
+  mkdir repo-git # or whatever
+  cd repo-git
+  git init
+  hg2git.sh <repo>
+
+Incremental imports to track hg repos is supported, too.
+
+Notes
+=====
+
+As there's no real config interface to hg2git.py (the worker script),
+checkpointing each 1000 changesets is hard-coded. "checkpointing" means
+to issue the "checkpoint" command of git-fast-import which then flushes
+the current pack file and starts a new one. This is sufficient for the
+initial import.
+
+However, per incremental import with fewer than 1000 changesets (read:
+most likely always), a new pack file will be created. Every time. As a
+consequence, the git repo should be repacked quite often.