add bouncy castle to libraries

content/docs/libraries.md

@@ -15,6 +15,9 @@ An open source C library for quantum-safe cryptographic algorithms.
 - [PQClean](https://github.com/PQClean/PQClean):
 Portable C implementations of post-quantum cryptography.
 
+- [The Legion of the Bouncy Castle](https://www.bouncycastle.org/specifications.html):
+Java implementation of cryptographic algorithms containing a light-weight API suitable for use in any environment.
+
 - [NaCL (Salt)](https://nacl.cr.yp.to/):
 Software library for network communication, encryption, decryption, signatures, etc.