add frf error in faq

src/content/docs/guides/faq.mdx

@@ -5,6 +5,7 @@ slug: guides/faq
 ---
 
 import { Steps } from '@astrojs/starlight/components';
+import imagefrf from '../../../assets/error_frf.png';
 
 ### **Q: Can I make the pipeline run in the background?**
 
@@ -16,3 +17,18 @@ The Nextflow `-bg` flag launches Nextflow in the background, detached from your
 
 Alternatively, you can use `screen` / `tmux` or similar tool to create a detached session which you can log back into at a later time.
 Some HPC setups also allow you to run nextflow within a cluster job submitted your job scheduler (from where it submits more jobs).
+
+### **Q: The module RECONST_FRF crashed. It can not find a minimum number of voxels to identify as single-fiber voxels in automatic estimation**
+
+<div class="centered">
+  <img src={imagefrf.src} alt="screenshot of the FRF module crash" />
+</div>
+
+This is an example illustrated a failure of the FRF module caused by an insufficient number of voxels identified as single-fiber voxels during an automatic estimation.
+In this case, only 16 voxels were detected.
+By default, the minimum required number of voxels is **100** for this pipeline, depending on the resolution or the quality of the data, a higher threshold may be necessary. 
+
+To lower this requirement, you can specify a small value using `--nvox_min=X` option in your command line. 
+
+For this exemple:
+`--nvox_min=10`.