Add readme.md

README.md

+# Purpose
+
+This repository is used for put the business template which not suitable to put
+in the main nexedi/erp5 repository, such as large files(exceeds 100 MB).
+
+SlapOS was configured to use erp5-bin as external repository:
+https://lab.nexedi.com/nexedi/slapos/blob/master/stack/erp5/buildout.cfg#L346
+
+So this external library was managed by SlapOS. Updating work also done by SlaOS.
+
+# Submodule
+
+Use git submodule needs to pin a revision in the main erp5 repository. Each time
+we commit something to the submodule, we also need to update the revision, which
+add a redundent commit in the main erp5 repository.
+
+If we use submodule, people have two choices. The first one is to execute git
+commands from terminals. The second one is improve the erp5_forge bt. Which also
+bring a new issue: When checkout branch in erp5 repository, how to handle the
+submodule. Add a hook like post-call to re-initialize the submodule, or done it
+manually from command line?
+
+Last but not least. The submodule not managed by SlapOS. Use external repository
+can force people to use SlapOS.
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