Add ad-hoc FRU section to the tlbmc onboarding guide.

PiperOrigin-RevId: 745354806
Change-Id: I30de2e57cbacadcd1e652d07784aa1059faa66f4
diff --git a/tlbmc/g3doc/general/onboarding_npis.md b/tlbmc/g3doc/general/onboarding_npis.md
index 9384873..798d8c4 100644
--- a/tlbmc/g3doc/general/onboarding_npis.md
+++ b/tlbmc/g3doc/general/onboarding_npis.md
@@ -267,6 +267,44 @@
 ...
 ```
 
+### Ad-Hoc Frus
+
+Certain FRUs require special handling as they may not be scannable when bmcweb
+comes up. For this purpose, we have created something called an "Ad-Hoc Fru
+Scanner". This will allow you to configure exactly how you want to scan a FRU.
+
+An example is below:
+
+```
+        "AdHocFruConfig": {
+            "name": "AdHocFru",
+            "i2c_common_config": {
+                "bus": "4",
+                "address": "83"
+            },
+            "delay_between_reads": "0.001s",
+            "periodic_scan_config": [
+                {
+                    "scan_interval": "10s",
+                    "scan_count": 6
+                },
+                {
+                    "scan_interval": "60s",
+                    "scan_count": 9
+                },
+                {
+                    "scan_interval": "600s",
+                    "scan_count": 5
+                }
+            ]
+        }
+```
+
+The proto definition is found
+[here](https://gbmc.googlesource.com/gbmcweb/+/refs/heads/master/tlbmc/ad_hoc_fru_config.proto).
+
+> NOTE: This must go inside the ProbeV2 Json Object.
+
 ## Sensor
 
 ### HWMon Sensors