Update ERD diagram to schema 210

- Reflect changes since schema 209
- Updated image for Developer's guide
- Improve README file
  - Update MySQLWorkbench version
  - Update download link
  - Add instructions to update latest PDF symlink
  - Minor formatting adjustments

Fixes #26098

docbook/erd/README.md

@@ -1,12 +1,12 @@
 The MantisBT Entity-Relationship Diagram
 ========================================
 
-The diagram was built using MySQL Workbench [1] version 6.3.6. The MantisBT
+The diagram was built using MySQL Workbench [1] version 8.0.17. The MantisBT
 schema was reverse-engineered based on a freshly installed database, then the
 relationships between tables and corresponding cardinalities were manually
 added.
 
-[1] http://dev.mysql.com/downloads/tools/workbench/
+[1] https://dev.mysql.com/downloads/workbench/
 
 
 Editing Recommendations
@@ -37,25 +37,30 @@ Recommended naming convention for exported files:
 
 where
 
-  * VVV is the MantisBT version (e.g. 1.2)
-  * SSS is the corresponding schema version (e.g. 183)
-  * R indicates the diagram's revision number
-  * XXX is the file's extension (e.g. pdf, png)
+  * _VVV_ is the MantisBT version (e.g. 1.2)
+  * _SSS_ is the corresponding schema version (e.g. 183)
+  * _R_ indicates the diagram's revision number
+  * _XXX_ is the file's extension (e.g. pdf, png)
 
 
 Updating the Documentation
 --------------------------
 
-To keep the Developers Guide up-to-date as the ERD is modified:
+To keep the Developer's Guide up-to-date as the ERD is modified:
 
 1. Export the diagram as PNG
-2. Save the file in /docbook/Developers_Guide/en-US/images/erd.png
+2. Save the file in `/docbook/Developers_Guide/en-US/images/erd.png`
 3. Build the docbook and check that the updated file is there
 4. Commit changes
 
-Also remember to update the PDF on http://mantisbt.org/docs/erd
+Also remember to update the PDF on https://mantisbt.org/docs/erd
 
 1. Export the diagram as single-file PDF
 2. Save the file to a temp location as per above naming convention
 3. Upload the file to the server
 4. Remove the old file if necessary
+5. Update the symbolic link to the latest version of the PDF
+   ```
+    cd /path/to/docs/erd
+    ln -sf mantisbt_VVV_SSS_erd_rR.pdf latest.pdf 
+   ```