Add link to official serialization doc

Signed-off-by: Arthit Suriyawongkul <[email protected]>

Author: bact

src/spdx_tools/spdx3/writer/json_ld/process.md

@@ -1,5 +1,10 @@
 # Workflow
 
+Official SPDX v3.0 serialization documentation and context file
+are available at: <https://spdx.github.io/spdx-spec/v3.0/serializations/>
+
+## Manually generate context file
+
 Process to produce context file and a serialization example:
 
 1. Run
@@ -21,8 +26,6 @@ Process to produce context file and a serialization example:
     pyspdxtools3 -i  ./tests/spdx/data/SPDXJSONExample-v2.3.spdx.json -o example_with_context
     ```
 
-## Manually
-
 ## Known limitations
 
 - Validation of enums does not work