doc(pollux): verification policy documentation (#384)

pollux/docs/verification-policy.md

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+# Verification Policies [DRAFT]
+
+## Abstract
+This document describes the purpose, formats, and technical details of the Verification Policies implementation in the Atala Prism Platform.
+
+## 1. Introduction
+Verification Policies define the rules and constraints in the verification process between the Verifier and the Holder and applied to the Verifiable Credentials and Verifiable Presentation.
+
+Different rules and constraints can be defined and used based on the concrete implementation of the Verifiable Credentials.
+
+Verification Policies are the input for the [Presentation Definition](https://identity.foundation/presentation-exchange/spec/v2.0.0/#presentation-definition). 
+
+Examples of the rules the Verification Policies can articulate:
+- what proofs does the Verifier require
+- what issuers the Verifier trust
+- what Verifiable Credential format the Verifier requires
+
+## 2. Terminology
+#### Verification Policy
+The Verification Policy is a template that defines a set of constraints that the Verifier defines as verification rules.
+
+#### Issuer, Holder, Verifier
+These are well-known roles in the SSI domain.
+
+#### Party
+Party refers to any of the roles: Issuer, Holder, Verifier.
+
+## 3. Verification Policy structure
+#### id (UUID)
+The unique identifier of the entity
+
+---
+#### name (String)
+It is a human-readable name for the verification policy.
+
+---
+#### description (String)
+It is a human-readable description of the verification policy.
+
+---
+#### createdAt (DateTime)
+It's the date and time stamp of the verification policy creation.
+
+---
+#### updatedAt (DateTime)
+It's the date and time stamp of the verification policy update.
+
+---
+#### constraints (VerificationPolicyConstraint[])
+It's the defined set of constraints for the verification policy.
+
+---
+
+## 3. Verification Policy Constraints
+### 1. Credential Schema And Trusted Issuers
+It defines the credential schema and the list of trusted issuers and is
+applied to the JSON and JSON-LD verifiable credentials.
+Example:
+```
+{
+  "schemaId": "https://atala.io/credential-schemas/did:prism:shortid?id=abcde&version=1.0",
+  "trustedIssuers": [
+    "did:prism:trustedissueridentifier"
+  ]
+}
+```
+Given constraint defines the URL of the credential schema of the verifiable credentials a Holder must provide and the list of trusted issuers that issued the verifiable credential.
+
+## 4. Verification Policy Flows
+#### The Verifier creates the Verification Policy
+
+#### The Verifier requests the Verifiable Presentation from the Holder that includes the rules from the Verification Policy