Update EC overview doc for PUT path
Update EC overview doc for PUT path

Update the EC overview docs 'under the hood' section to reflect the
change in durable file parity from 2 to ec_nparity + 1 [1].

Also fix some typos and cleanup the text.

[1] change id I80d666f61273e589d0990baa78fd657b3470785d

Change-Id: I23f6299da59ba8357da2bb5976d879d9a4bb173e

tipabu/swift,prashanthpai/swift,revoer/keystone-8.0.0,notmyname/swift,psachin/swift,clayg/swift,swiftstack/swift,levythu/swift,matthewoliver/swift,dencaval/swift,clayg/swift,thiagodasilva/swift,redbo/swift,rackerlabs/swift,nadeemsyed/swift,larsbutler/swift,swiftstack/swift,matthewoliver/swift,nadeemsyed/swift,thiagodasilva/swift,smerritt/swift,openstack/swift,matthewoliver/swift,daasbank/swift,larsbutler/swift,bkolli/swift,psachin/swift,hbhdytf/mac2,mjwtom/swift,prashanthpai/swift,smerritt/swift,mjwtom/swift,hurricanerix/swift,redbo/swift,openstack/swift,tipabu/swift,notmyname/swift,hbhdytf/mac,notmyname/swift,levythu/swift,revoer/keystone-8.0.0,nadeemsyed/swift,psachin/swift,nadeemsyed/swift,psachin/swift,williamthegrey/swift,smerritt/swift,daasbank/swift,rackerlabs/swift,williamthegrey/swift,clayg/swift,openstack/swift,smerritt/swift,notmyname/swift,hbhdytf/mac2,matthewoliver/swift,openstack/swift,dencaval/swift,tipabu/swift,hbhdytf/mac2,swiftstack/swift,hurricanerix/swift,aerwin3/swift,hbhdytf/mac2,hbhdytf/mac,hurricanerix/swift,aerwin3/swift,tipabu/swift,bkolli/swift,hurricanerix/swift,clayg/swift