Added instructions on fetching replace objects for source history

README.md

@@ -127,6 +127,25 @@ The Factor source tree is organized as follows:
 * `misc/` - editor modes, icons, etc
 * `unmaintained/` - now at [factor-unmaintained](https://github.com/factor/factor-unmaintained)
 
+## Source History
+
+During Factor's lifetime, sourcecode has lived in many repositories. Unfortunately, the first import in Git did not keep history. History has been partially recreated from what could be salvaged. Due to the nature of Git, it's only possible to add history without disturbing upstream work, by using replace objects. These need to be manually fetched, or need to be explicitly added to your git remote configuration.
+
+Use:
+`git fetch origin 'refs/replace/*:refs/replace/*'`
+
+or add the following line to your configuration file
+
+```
+[remote "origin"]
+    url = ...
+    fetch = +refs/heads/*:refs/remotes/origin/*
+    ...
+    fetch = +refs/replace/*:refs/replace/*
+```
+
+Then subsequent fetches will automatically update any replace objects.
+
 ## Community
 
 Factor developers meet in the `#concatenative` channel on