docs: Add missing snitch_occupancy metric

Author: colluca

docs/ug/trace_analysis.md

@@ -128,6 +128,7 @@ In the following table you can find a complete list of all the performance metri
 |`snitch_issues`           |Total number of instructions issued by Snitch, excluding those offloaded to the FPSS (see `snitch_fseq_offloads`).                                                                                  |
 |`snitch_fseq_offloads`    |Total number of instructions offloaded by Snitch to the FPSS.                                                                                                                                       |
 |`snitch_fseq_rel_offloads`|The ratio between `snitch_fseq_offloads` and the total number of instructions issued by Snitch core proper, i.e. `snitch_issues + snitch_fseq_offloads`.                                            |
+|`snitch_occupancy`        |IPC of the Snitch core, calculated as `snitch_issues / cycles`.                                                                                                                                     |
 |`fpss_issues`             |Total number of instructions issued by the FPSS. It counts repeated issues from the FREP sequencer.                                                                                                 |
 |`fpss_fpu_issues`         |Similar to `fpss_issues`, but counts only instructions destined to the FPU proper. It does not for instance include instructions issued to the FPSS's LSU.                                          |
 |`fseq_yield`              |The ratio between `fpss_issues` and `snitch_fseq_offloads`. The difference lies in the FREP sequencer possibly replicating instructions. If the sequencer is not used this ratio should amount to 1.|