Merge pull request #913 from vitzli/master

add /dev/crypto-notes.md

dev/crypto-notes.md

+## Important notes
+
+### Key-pair generation
+
+It is critical that we check cryptographic operations to ensure the right amount of entropy is being sourced.
+See: [Issue #911](https://github.com/jbenet/go-ipfs/issues/911)
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