minor improvements to chapter "Payment Hash" and "Additional Meta Data" (#198)

- repeated use of "also", --> furthermore, ...
- minor clarifications
- etc

ch03.asciidoc

@@ -305,16 +305,16 @@ The payee will choose a truly random number `r` and produces the `sha256` of tha
 Note that an adversary should have no means of guessing or predicting `r`.
 Using a customer id or the hash of entries of the shopping cart together with a timestamp is not truly random and yields a security risk.
 The payment process of the Lightning Network is only secure if `r` is chosen completely randomly and is not predictable and as long as the Hash function cannot be inverted.
-We note that this is not an additional security assumption for Bitcoin as the security of the Hash function is currently what Bitcoin mining is built upon.
+We note that this is not an additional security assumption for Bitcoin as the security of the Hash function is currently the underlying basis of Bitcoin mining.
 
 ==== Additional Meta Data
 Invoices can encode some other useful meta data.
 For example a short description.
-In case a user has several invoices to pay, the user can read the description and make sure what the invoice was about.
+In case a user has several invoices to pay, the user can read the description and be reminded what the invoice is about.
 As payment channels do not need to be publicly announced, the payee can also provide some private channels as routing hints to the invoice.
-These hints can also be used for public channels to point to those channels on which the payee has enough inbound liquidity to actually receive the amount.
-In case the payer's Lightning node is not able to send the payment over the Lightning Network, invoices can also include a fallback address.
-We would however always recommend to open a new payment channel instead of doing an on-chain transaction that does not add an additional payment channel.
+These hints can furthermore be used to suggest public channels, e.g. those channels on which the payee has enough inbound liquidity to actually receive the amount.
+In case the payer's Lightning node is not able to send the payment over the Lightning Network, invoices can optionally include an on-chain Bitcoin fallback address.
+We would however always recommend to open a new Lightning payment channel instead of doing an on-chain Bitcoin payment.
 Invoices also have an expiry time so that the payee can delete the preimage after some time to free up space.
 
 === Delivering the payment