add some class diagrams

Author: kmurphypolygon

docs/img/cdk/high-level-architecture/bridging-class-diagram.png

@@ -1,3 +1,5 @@
+![Polygon Solidity smart contract bridging architecture](../../../../img/cdk/high-level-architecture/bridging-class-diagram.png)
+
 The unified bridge transfers assets and messages between networks (L1, L2) by calling bridge and claim functions on the [PolygonZkEVMBridgeV2.sol](https://github.com/0xPolygonHermez/zkevm-contracts/blob/main/contracts/v2/PolygonZkEVMBridgeV2.sol) contract whose deployment address is an [upgradeable proxy](https://etherscan.io/address/0x2a3DD3EB832aF982ec71669E178424b10Dca2EDe#code). Interaction with the actual contract happens via the proxy.
 
 This contract is deployed on L1 and there is also one deployed on every L2 network. It communicates closely with an exit root manager contract specific to L1 or L2.

docs/img/cdk/high-level-architecture/overview-class-diagram.png

@@ -1,3 +1,5 @@
+![Polygon Solidity smart contract bridging architecture](../../../../img/cdk/high-level-architecture/bridging-class-diagram.png)
+
 An exit tree is a binary, append-only, sparse Merkle tree (SMT) whose leaf nodes store bridging data. The exit trees have a depth of 32.
 
 The Merkle root of an exit tree is known as the exit tree root, and it is the fingerprint of all the information recorded in the exit tree's leaf nodes. 

docs/img/cdk/high-level-architecture/smart-contracts-full-view.png

@@ -2,16 +2,22 @@
 comments: true
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-<!-- https://excalidraw.com/#json=JKZp9QEihifF_B7Z41Dfv,FVNhqQKi9PA1jM0kzUoCsQ" -->
+The skeleton-class diagram below reveals the smart contract architecture of rollup and CDK stacks.
+
+![Polygon Solidity smart contract architecture full view](../../../../img/cdk/high-level-architecture/overview-class-diagram.png)
 
 ## Polygon smart contract architecture
 
 Chain stacks at the node level direct transaction data to the L2 and L1 networks via smart contract calls. The system stores state in binary tree structures containing verifiable local and global exit roots.
 
-The diagram below details the Polygon Solidity smart contract architecture. 
+The diagram below details the Polygon Solidity smart contract architecture minus the bridging contracts. 
 
 ![Polygon Solidity smart contract architecture](../../../../img/cdk/high-level-architecture/smart-contracts-full-view.png)
 
+And here is the class diagram for the unified bridge and exit roots activity.
+
+![Polygon Solidity smart contract bridging architecture](../../../../img/cdk/high-level-architecture/bridging-class-diagram.png)
+
 There are four key contract types built into the system design: 
 
 - The [consensus contract set](#consensus-contracts).