Add "epoch summary" command.

docs/usage.md

@@ -407,6 +407,37 @@ Deposit commands focus on information about deposit data information in a JSON f
 $ ethdo deposit verify --data=${HOME}/depositdata.json --withdrawalpubkey=0xad1868210a0cff7aff22633c003c503d4c199c8dcca13bba5b3232fc784d39d3855936e94ce184c3ce27bf15d4347695 --validatorpubkey=0xa951530887ae2494a8cc4f11cf186963b0051ac4f7942375585b9cf98324db1e532a67e521d0fcaab510edad1352394c --depositvalue=32Ether
 ```
 
+### `epoch` comands
+
+Epoch commands focus on information about a beacon chain epoch.
+
+#### `summary`
+
+`ethdo epoch summary` provides a summary of the given epoch.  Options include:
+  - `epoch`: the epoch for which to provide a summary; defaults to last complete epoch
+  - `json`: provide JSON output
+
+```sh
+$ ethdo epoch summary
+Epoch 1406:
+  Slot 44992 (0/32):
+    Proposer: 31501
+    Proposed: ✓
+  Slot 44993 (1/32):
+    Proposer: 9302
+    Proposed: ✓
+  ...
+  Sync committee validator 71248:
+    Chances: 29
+    Included: 7
+    Inclusion %: 24.14
+  Sync committee validator 87371:
+    Chances: 29
+    Included: 0
+    Inclusion %: 0.00
+  ...
+```
+
 ### `exit` comands
 
 Exit commands focus on information about validator exits generated by the `ethdo validator exit` command.