docs: remove the ppa reference from the docs

Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

README.md

@@ -39,21 +39,10 @@ Pruning (`prune=n` option in `bitcoin.conf`) is partially supported, see [here](
 
 There are 4 supported installation options:
 
- - Installation from the [Ubuntu PPA][ppa].
  - Installation of a pre-compiled binary from the [release page][releases] on GitHub.
  - Using one of the [provided docker images][dockerhub] on the Docker Hub.
  - Compiling the source code yourself as described in the [installation documentation](doc/INSTALL.md).
 
-For the impatient here's the gist of it for Ubuntu:
-
-```bash
-sudo apt-get install -y software-properties-common
-sudo add-apt-repository -u ppa:lightningnetwork/ppa
-sudo apt-get install lightningd snapd
-sudo snap install bitcoin-core
-sudo ln -s /snap/bitcoin-core/current/bin/bitcoin{d,-cli} /usr/local/bin/
-```
-
 ### Starting `lightningd`
 
 #### Regtest (local, fast-start) Option
@@ -237,7 +226,6 @@ You should also configure with `--enable-developer` to get additional checks and
 [discord]: https://discord.gg/mE9s4rc5un
 [telegram]: https://t.me/lightningd
 [docs]: https://lightning.readthedocs.org
-[ppa]: https://launchpad.net/~lightningnetwork/+archive/ubuntu/ppa
 [releases]: https://github.com/ElementsProject/lightning/releases
 [dockerhub]: https://hub.docker.com/r/elementsproject/lightningd/
 [jsonrpcspec]: https://www.jsonrpc.org/specification