docs: use dummy var to make autodoc work (#82)

close #73 

just use a dummy var so the module chills out

I don't totally love the way this works right now, but this is a simple
fix for now

Author: jsstevenson

docs/source/conf.py

@@ -73,3 +73,8 @@ def linkcode_resolve(domain, info):
 # -- code block style --------------------------------------------------------
 pygments_style = "default"
 pygements_dark_style = "monokai"
+
+# -- set default env vars ----------------------------------------------------
+import os
+
+os.environ.setdefault("BEACON_NODE_ID", "docs_dummy_beacon_node_id")