minor improvements

- README: add matrix room

- examples/configuration.nix: explain why bitcoind is enabled by default

- btcpayserver: group lnd service settings

- clightning:
  Use public onion port only when the onion service is public

  This allows users to enable the onion service while announcing a
  non-onion public address.

- netns-isolation: move `readOnly` attr to the top

- tests: use mkDefault to allow for easier overriding

- tests/btcpayserver: test web server response

test/tests.py

@@ -201,6 +201,8 @@ def _():
         f"-X GET https://{ip('lnd')}:8080/v1/getinfo | jq",
         '"version"',
     )
+    # Test web server response
+    assert_matches(f"curl -L {ip('btcpayserver')}:23000", "Welcome to your BTCPay Server")
 
 @test("spark-wallet")
 def _():