diff --git a/README.md b/README.md
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+++ b/README.md
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 This repository contains the documentations for various CPUs. It contain data sheets, programmer's manuals, quick reference cards, and the like.
 
+Before submitting a pull request, [Contribution Guildelines](contributing.md).
+
 | Subfolders | Description |
 | ---------- | ----------- |
 | 8085 | Intel 8085 |
diff --git a/contributing.md b/contributing.md
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+## Contibution Guidelines
+
+Documentation for new CPUs or MCUs are happily accepted.  It's
+preferred to add processor family architecture documents.  
+
+The GitHub 1G size limit on repositories is a concern.  If a
+subdirectory grows large, please add it as a git submodule.  The
+submodule repository should belong to the
+[awesome-cpus](https://github.com/awesome-cpus) origanization.
+Everyone are welcome to join.