docs: add Internal.UnixFSShardingSizeThreshold (#8723)

Co-authored-by: Marcin Rataj <lidel@lidel.org>

docs/config.md

@@ -16,6 +16,7 @@ config file at runtime.
     - [`strings`](#strings)
     - [`duration`](#duration)
     - [`optionalInteger`](#optionalinteger)
+    - [`optionalBytes`](#optionalbytes)
     - [`optionalString`](#optionalstring)
     - [`optionalDuration`](#optionalduration)
   - [`Addresses`](#addresses)
@@ -67,6 +68,7 @@ config file at runtime.
       - [`Internal.Bitswap.EngineBlockstoreWorkerCount`](#internalbitswapengineblockstoreworkercount)
       - [`Internal.Bitswap.EngineTaskWorkerCount`](#internalbitswapenginetaskworkercount)
       - [`Internal.Bitswap.MaxOutstandingBytesPerPeer`](#internalbitswapmaxoutstandingbytesperpeer)
+    - [`Internal.UnixFSShardingSizeThreshold`](#internalunixfsshardingsizethreshold)
   - [`Ipns`](#ipns)
     - [`Ipns.RepublishPeriod`](#ipnsrepublishperiod)
     - [`Ipns.RecordLifetime`](#ipnsrecordlifetime)
@@ -278,6 +280,15 @@ an implicit default when missing from the config file:
 - `null`/missing will apply the default value defined in go-ipfs sources (`.WithDefault(value)`)
 - an integer between `-2^63` and `2^63-1` (i.e. `-9223372036854775808` to `9223372036854775807`)
 
+### `optionalBytes`
+
+Optional Bytes allow specifying some number of bytes which has
+an implicit default when missing from the config file:
+
+- `null`/missing (apply the default value defined in go-ipfs sources)
+- a string value indicating the number of bytes, including human readable representations:
+  - [SI sizes](https://en.wikipedia.org/wiki/Metric_prefix#List_of_SI_prefixes) (metric units, powers of 1000), e.g. `1B`, `2kB`, `3MB`, `4GB`, `5TB`, …)
+  - [IEC sizes](https://en.wikipedia.org/wiki/Binary_prefix#IEC_prefixes) (binary units, powers of 1024), e.g. `1B`, `2KiB`, `3MiB`, `4GiB`, `5TiB`, …)
 
 ### `optionalString`
 
@@ -287,7 +298,6 @@ an implicit default when missing from the config file:
 - `null`/missing will apply the default value defined in go-ipfs sources (`.WithDefault("value")`)
 - a string
 
-
 ### `optionalDuration`
 
 Optional durations allow specifying some duration value which has
@@ -940,6 +950,18 @@ deteriorate the quality provided to less aggressively-wanting peers.
 
 Type: `optionalInteger` (byte count, `null` means default which is 1MB)
 
+### `Internal.UnixFSShardingSizeThreshold`
+
+The sharding threshold used internally to decide whether a UnixFS directory should be sharded or not.
+This value is not strictly related to the size of the UnixFS directory block and any increases in
+the threshold should come with being careful that block sizes stay under 2MiB in order for them to be
+reliably transferable through the networking stack (IPFS peers on the public swarm tend to ignore requests for blocks bigger than 2MiB).
+
+Decreasing this value to 1B is functionally equivalent to the previous experimental sharding option to
+shard all directories.
+
+Type: `optionalBytes` (`null` means default which is 256KiB)
+
 ## `Ipns`
 
 ### `Ipns.RepublishPeriod`