[Frama-PLC] updates the user's manual

3 jobs for frama-plc in 1 minute and 44 seconds (queued for 4 seconds)
Name Stage Failure
failed
test Test
      Generating... 
Jekyll Feed: Generating feed for posts
Liquid Exception: Could not find document '_online-docs/frama-plc/frama-plc-user-manual.md' in tag 'link'. Make sure the document exists and the path is correct. in /builds/pub/pub.frama-c.com/_fc-plugins/frama-plc.md
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Jekyll 4.0.0 Please append `--trace` to the `build` command
for any additional information or backtrace.
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Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1