Adds preproduction warning

README.md

@@ -22,6 +22,16 @@
 
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+## Pre-production warning
+
+This software is a pre-release version which has not yet been audited and therefore should not yet be trusted to keys with the intent of securing actual ETH.
+
+### BLS versioning
+
+The eth2specs changed their BLS version from [BLS v0](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-00), and [hash to curve v4](https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-04) to [BLS v2](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-02), and [hash to curve v7](https://tools.ietf.org/html/draft-irtf-cfrg-hash-to-curve-07). Because of this this version of the deposit CLI, is not compatible with eth2 versions >= `0.12.x` which includes main net.
+
+**Using this version for Mainnet deposits will result in loss of funds**
+
 ## Tutorial for users
 
 ### Requirements