Add package extraction notes

License: MIT
Signed-off-by: Lars Gierth <larsg@systemli.org>

README.md

@@ -53,3 +53,55 @@ $ go test ./p2p/<path of module you want to run tests for>
 ## Links
 - [**Specs**](https://github.com/ipfs/specs/tree/master/libp2p)
 - [**Website**](https://github.com/diasdavid/libp2p-website)
+
+
+## Extracting packages from go-libp2p
+
+We want to maintain history, so we'll use git-subtree for extracting packages.
+
+```sh
+# 1) create the extracted tree (has the directory specified as -P as its root)
+> cd go-libp2p/
+> git subtree split -P p2p/crypto/secio/ -b libp2p-secio
+62b0a5c21574bcbe06c422785cd5feff378ae5bd
+# important to delete the tree now, so that outdated imports fail in step 5
+> git rm -r p2p/crypto/secio/
+> git commit
+> cd ../
+
+# 2) make the new repo
+> mkdir go-libp2p-secio
+> cd go-libp2p-secio/
+> git init && git commit --allow-empty
+
+# 3) fetch the extracted tree from the previous repo
+> git remote add libp2p ../go-libp2p
+> git fetch libp2p
+> git reset --hard libp2p/libp2p-secio
+
+# 4) update self import paths
+> sed -someflagsidontknow 'go-libp2p/p2p/crypto/secio' 'golibp2p-secio'
+> git commit
+
+# 5) create package.json and check all imports are correct
+> vim package.json
+> gx --verbose install --global
+> gx-go rewrite
+> go test ./...
+> gx-go rewrite --undo
+> git commit
+
+# 4) make the package ready
+> vim README.md LICENSE
+> git commit
+
+# 5) bump the version separately
+> vim package.json
+> gx publish
+> git add package.json .gx/
+> git commit -m 'Publish 1.2.3'
+
+# 6) clean up and push
+> git remote rm libp2p
+> git push origin master
+```