doc: Add note to fpgadiag --freq option
Add a note to the --freq option to indicate that the command line option
is used only when the software cannot infer the frequency from the AFU.
@@ -114,7 +114,11 @@ on the platform.
`--freq=, -T`
- Clock frequency in Hz. The default=400000000 Hz (400 MHz).
+ Clock frequency (in Hz) used for bandwidth calculation. The default=400000000 Hz (400 MHz).
+```eval_rst
+.. note::
+ This frequency is used only when the software cannot infer the frequency from the accelerator.
+```
`--suppress-hdr, -S`
