add DID workflow mermaid charts

Signed-off-by: Chuck Adams <chaz@chaz.works>

Author: chuckadams

docs/flowcharts/did-workflows.md

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+# DID Workflows
+
+# did:plc
+
+```mermaid
+flowchart TD
+    A1["Install: Get package did:plc from user input"]
+    A2["Update: Resolve package did:plc from header comment"]
+    A1 --> B["Fetch DID Document from plc.directory"]
+    A2 --> B
+    B --> C{"DID verification enabled?"}
+    C -- Yes --> D["Fetch PLC audit log: plc.directory/$did/log/audit"]
+    D --> E["Hash genesis op"]
+    E --> F["Verify DID match"]
+    F --> G["Recompute CID of each op"]
+    G --> H["Verify ECDSA with prior keys"]
+    H --> I["Derive verificationMethods & services"]
+    I --> J{Valid?}
+    J -- No --> X1[Fail: Invalid DID verification]
+    J -- Yes --> K["Select #fairpm publicKeyMultibase key"]
+    C -- No --> K["Select #fairpm publicKeyMultibase key"]
+    K --> L["Select FairPackageManagementRepo URL from serviceEndpoint"]
+    L --> M["Download package ZIP from FairPackageManagementRepo"]
+    M --> N["Calculate package ZIP file SHA384 hash"]
+    M --> O["Extract package signature from ZIP download HTTP response header"]
+    N --> P{"Verify calculated SHA384 signature"}
+    O --> P
+    P -- No --> X2["Fail: Invalid package signature"]
+    P -- Yes --> Q["Success: install/update package"]
+```
+
+#  
+
+```mermaid
+flowchart TD
+A1["Install: Get package did:web from user input"]
+A2["Update: Resolve did:web from package header comment"]
+A1 --> B["Construct DID Document URL from did:web"]
+A2 --> B
+B --> C["Fetch DID Document via HTTPS"]
+C --> D["Select #fairpm publicKeyMultibase key"]
+D --> E["Select FairPackageManagementRepo URL from serviceEndpoint"]
+E --> F["Download package ZIP from FairPackageManagementRepo"]
+F --> G["Calculate package ZIP file SHA384 hash"]
+F --> H["Extract package signature from ZIP download HTTP response header"]
+G --> I{"Verify calculated SHA384 signature"}
+H --> I
+I -- Invalid --> X1["Fail: Invalid package signature"]
+I -- Valid --> J["Success: install/update package"]
+```