docs: update intro and add spec list (#1411)

Signed-off-by: Rolson Quadras <[email protected]>

README.md

@@ -8,11 +8,22 @@
 
 # TrustBloc VCS
 
-TrustBloc Verifiable Credential Service (VCS) project provides following services for [W3C Verifiable Credentials (VC)](https://www.w3.org/TR/vc-data-model/) based on [W3C-CCG VC API](https://w3c-ccg.github.io/vc-api/).
-- [Issuer](https://w3c-ccg.github.io/vc-api/#issuing)
-- [Verifier](https://w3c-ccg.github.io/vc-api/#verifying) 
-- [Holder](https://w3c-ccg.github.io/vc-api/#presenting)
-
+The TrustBloc Verifiable Credential Service (VCS) repo contains APIs to Issue and Verify 
+[W3C Verifiable Credentials(VCs)](https://www.w3.org/TR/vc-data-model/) signed using 
+[W3C Decentralized Identifiers(DIDs)](https://www.w3.org/TR/did-core/). These APIs are useful for 
+the Issuer and Verifier role defined in the [W3C VC Specification](https://www.w3.org/TR/vc-data-model/#ecosystem-overview).
+
+## Specifications
+
+The TrustBloc VCS implements following specifications.
+- W3C [Verifiable Credential Data Model (VCDM)](https://www.w3.org/TR/vc-data-model/)
+- W3C [Decentralized Identifier (DID)](https://www.w3.org/TR/did-core/)
+- OIDF [OpenID for Verifiable Credential Issuance](https://openid.net/specs/openid-4-verifiable-credential-issuance-1_0.html)
+    - Pre Authorization Code flow
+    - Authorization Code low
+- OIDF [OpenID for Verifiable Presentation](https://openid.net/specs/openid-4-verifiable-presentations-1_0.html)
+- DIF [Presentation Exchange](https://identity.foundation/presentation-exchange/)
+- DIF [Well Known DID Configuration](https://identity.foundation/.well-known/resources/did-configuration/)
 
 ## Build
 To build from source see [here](docs/build.md).