message: Improve doc/i2p.md regarding I2P router options/versions
diff: @@ -10,11 +10,22 @@ started with I2P terminology.
  ## Run Bitcoin Core with an I2P router (proxy)
  A running I2P router (proxy) with [SAM](https://geti2p.net/en/docs/api/samv3)
  -enabled is required (there is an [official one](https://geti2p.net) and
  -[a few alternatives](https://en.wikipedia.org/wiki/I2P#Routers)). Notice the IP
  -address and port the SAM proxy is listening to; usually, it is
  -`127.0.0.1:7656`. Once it is up and running with SAM enabled, use the following
  -Bitcoin Core options:
  +enabled is required. Options include:
  +
  +- [i2prouter (I2P Router)](https://geti2p.net), the official implementation in
  + Java
  +- [i2pd (I2P Daemon)](https://github.com/PurpleI2P/i2pd)
  + ([documentation](https://i2pd.readthedocs.io/en/latest)), a lighter
  + alternative in C++ (successfully tested with version 2.23 and up; version 2.36
  + or later recommended)
  +- [i2p-zero](https://github.com/i2p-zero/i2p-zero)
  +- [other alternatives](https://en.wikipedia.org/wiki/I2P#Routers)
  +
  +Note the IP address and port the SAM proxy is listening to; usually, it is
  +`127.0.0.1:7656`.
  +
  +Once an I2P router with SAM enabled is up and running, use the following Bitcoin
  +Core configuration options:
  ```
  -i2psam=<ip:port>
  