Add README.md to project

Author: npaun

README.md

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+# Node.js crypto (ncrypto) library
+
+The `ncrypto` library extracts the base internal implementation of Node.js crypto operations
+that support both `node:crypto` and Web Crypto implementations and makes them available for
+use in other projects that need to emulate Node.js' behavior.
+
+## Compatibility
+
+* Build systems: `ncrypto` can be built with either Bazel or CMake.
+* SSL libraries: `ncrypto` supports linking to either `boringssl` or `openssl`.
+
+## Build flags
+
+* Bazel: `--@ncrypto//:bssl_libdecrepit_missing=True` 
+* CMake: `-DNCRYPTO_BSSL_LIBDECREPIT_MISSING=1`
+
+If linking against `boringssl`, libdecrepit is an optional component that isn't always built. If
+this option is set, `ncrypto` will use a built-in replacement for the missing functions.