addition to chapter "Commonality of Bitcoin and Lightning" (#210)

* addition to chapter "Commonality of Bitcoin and Lightning"

- as contrast to chapter of differences between Bitcoin and Lightning
- a lot is missing here
- this is just an initial draft to get the ball rolling and other contributors can add
- even if these things have been mentioned somewhere throughout the book it is useful to gather them here as a summarized list. People looking thru the TOC can find this chapter and it will give them (hopefully) a good overview of commonalities

* added to chapter "Commonality of Bitcoin and Lightning" 

- added a few more bullet points
- more are still missing ....

* Milli-satoshis and trustlessness

- see https://github.com/lnbook/lnbook/pull/210#discussion_r420515887
- see https://github.com/lnbook/lnbook/pull/210#discussion_r420516103

ch03.asciidoc

@@ -709,3 +709,41 @@ That node must be "online" at the time of the payment.
 To be precise, both nodes, the payer's and the payee's must be online at the time of payment.
 The payer and payee must cooperate, i.e. in some fashion one could say "synchronize" , during the payment. 
 If the payee's node is down the payer cannot make the payment.
+
+==== Satoshis vs. Milli-Satoshis
+On Bitcoin the smallest amount is a "satoshi" which cannot be divided any further.
+Lightning can be more flexible. 
+Lightning nodes can optionally be configured to work with "milli-satoshis". 
+So, within Lightning even smaller amounts can be exchanged. 
+When settled on-chain, it must be settled in "satoshis".
+
+=== Commonality of Bitcoin and Lightning
+
+==== Monetary Unit
+
+Both the Bitcoin network and the Lightning network use the same monetary units: bitcoins. 
+Lightning payments use the very same bitcoins as Bitcoin transactions.
+
+==== Irrevocability 
+
+Both, Bitcoin transactions and Lightning payments are irrevocable. 
+There is no "undo" operation for either one. 
+As a user of either one you have to act responsibly.
+
+==== Trustlessness
+
+Just as Bitcoin, Lightning requires the user only to trust mathematics, encryption and that the Lightning code does not have any critical bugs.
+Neither Bitcoin nor Lightning require the user to trust a person, a company, an institution or a government.
+Since Lightning sits on top of Bitcoin and relies on Bitcoin as its underlying base layer, it is clear that the security model of Lightning reduces to the security of the base blockchain. 
+In other words, Lightning can never be more trustless than Bitcoin.
+
+==== Permissionlessness
+
+Both Bitcoin and Lightning can be used by anybody with access to the Internet and to the appropriate software, e.g. node and wallet. 
+The user of neither network requires permission from third-party persons, companies, institutions or a government.
+The user does not need permission from anybody as long as he has access to Internet and can run his node or wallet.
+Governments can only outlaw Bitcoin or Lightning locally in their jurisdiction, but they cannot prevent their global use.
+
+==== Open Source
+
+Both, Bitcoin and Lightning are open source software and are built by a decentralized global community on open source principles.