Added sharding to experimental features

Not sure about "Road to being a real feature" and also would like to have
clarified when this is being used. My understanding is that it'll shard
automatically both when using the Files API and also when doing `ipfs add -r`
but I'm not 100% about this.

License: MIT
Signed-off-by: Victor Bjelkholm <victorbjelkholm@gmail.com>

docs/experimental-features.md

@@ -343,3 +343,25 @@ See [Plugin docs](./plugins.md)
 
 - [ ] Needs more testing
 - [ ] Make sure there are no unknown major problems
+
+## Directory Sharding / HAMT
+
+### In Version
+0.4.8
+
+### State
+Experimental
+
+Allows to create directories with unlimited number of entries - currently
+size of unixfs directories is limited by the maximum block size
+
+### Basic Usage:
+
+```
+ipfs config --json Experimental.ShardingEnabled true
+```
+
+### Road to being a real feature
+
+- [ ] Make sure that objects that don't have to be sharded aren't
+- [ ] Generalize sharding and define a new layer between IPLD and IPFS