doc: I2P documentation updates

doc/i2p.md

@@ -33,12 +33,10 @@ configuration options:
      none)
 
 -i2pacceptincoming
-     If set and -i2psam is also set then incoming I2P connections are
-     accepted via the SAM proxy. If this is not set but -i2psam is set
-     then only outgoing connections will be made to the I2P network.
-     Ignored if -i2psam is not set. Listening for incoming I2P
-     connections is done through the SAM proxy, not by binding to a
-     local address and port (default: 1)
+     Whether to accept inbound I2P connections (default: 1). Ignored if
+     -i2psam is not set. Listening for inbound I2P connections is
+     done through the SAM proxy, not by binding to a local address and
+     port.
 ```
 
 In a typical situation, this suffices:
@@ -56,6 +54,36 @@ connections if `-i2pacceptincoming=1`. If `-i2pacceptincoming=0` then only
 outbound I2P connections are made and a different transient I2P address is used
 for each connection to improve privacy.
 
+## Additional configuration options related to I2P
+
+```
+-debug=i2p
+```
+
+Set the `debug=i2p` config logging option to see additional information in the
+debug log about your I2P configuration and connections.
+
+```
+-onlynet=i2p
+```
+
+Make automatic outbound connections only to I2P addresses. Inbound and manual
+connections are not affected by this option. It can be specified multiple times
+to allow multiple networks, e.g. onlynet=onion, onlynet=i2p.
+
+I2P support was added to Hush in version 3.9.3 and there may be fewer I2P
+peers than Tor or IP ones. Therefore, using I2P alone without other networks may
+make a node more susceptible to [Sybil
+attacks](https://en.bitcoin.it/wiki/Weaknesses#Sybil_attack). 
+
+Another consideration with `onlynet=i2p` is that the initial blocks download
+phase when syncing up a new node can be very slow. This phase can be sped up by
+using other networks, for instance `onlynet=onion`, at the same time.
+
+In general, a node can be run with both onion and I2P hidden services (or
+any/all of IPv4/IPv6/onion/I2P/CJDNS), which can provide a potential fallback if
+one of the networks has issues.
+
 ## Persistent vs transient I2P addresses
 
 In I2P connections, the connection receiver sees the I2P address of the
@@ -136,14 +164,19 @@ port (`TO_PORT`) is always set to 0 and is not in the control of Hush.
 
 ## Bandwidth
 
-I2P routers may route a large amount of general network traffic with their
-default settings. Check your router's configuration to limit the amount of this
-traffic relayed, if desired.
+By default, your node shares bandwidth and transit tunnels with the I2P network
+in order to increase your anonymity with cover traffic, help the I2P router used
+by your node integrate optimally with the network, and give back to the network.
+It's important that the nodes of a popular application like Hush contribute
+as much to the I2P network as they consume.
 
-With `i2pd`, the amount of bandwidth being shared with the wider network can be
-adjusted with the `bandwidth`, `share` and `transittunnels` options in your
-`i2pd.conf` file. For example, to limit total I2P traffic to 256KB/s and share
-50% of this limit for a maximum of 20 transit tunnels:
+It is possible, though strongly discouraged, to change your I2P router
+configuration to limit the amount of I2P traffic relayed by your node.
+
+With `i2pd`, this can be done by adjusting the `bandwidth`, `share` and
+`transittunnels` options in your `i2pd.conf` file. For example, to limit total
+I2P traffic to 256KB/s and share 50% of this limit for a maximum of 20 transit
+tunnels:
 
 ```
 bandwidth = 256
@@ -153,9 +186,15 @@ share = 50
 transittunnels = 20
 ```
 
-If you prefer not to relay any public I2P traffic and only permit I2P traffic
-from programs which are connecting via the SAM proxy, e.g. Hush, you
-can set the `notransit` option to `true`.
-
 Similar bandwidth configuration options for the Java I2P router can be found in
 `http://127.0.0.1:7657/config` under the "Bandwidth" tab.
+
+Before doing this, please see the "Participating Traffic Considerations" section
+in [Embedding I2P in your Application](https://geti2p.net/en/docs/applications/embedding).
+
+In most cases, the default router settings should work fine.
+
+## Bundling I2P in a Hush application
+
+Please see the "General Guidance for Developers" section in https://geti2p.net/en/docs/api/samv3
+if you are developing a downstream application that may be bundling I2P with Hush.