Update README.md

Error in ubuntu repo installation command for not super user. Sudo command works only for echo command not for redirection and plain user have no rights to write to /etc/apt/sources.list.d/ folder.

Author: dld-r00f

README.md

@@ -72,7 +72,7 @@ Installers are available in release **assets**. [Latests](https://github.com/pos
 #### pg_probackup for vanilla PostgreSQL
 ```shell
 #DEB Ubuntu|Debian Packages
-sudo echo "deb [arch=amd64] https://repo.postgrespro.ru/pg_probackup/deb/ $(lsb_release -cs) main-$(lsb_release -cs)" > /etc/apt/sources.list.d/pg_probackup.list
+sudo sh -c 'echo "deb [arch=amd64] https://repo.postgrespro.ru/pg_probackup/deb/ $(lsb_release -cs) main-$(lsb_release -cs)" > /etc/apt/sources.list.d/pg_probackup.list'
 sudo wget -O - https://repo.postgrespro.ru/pg_probackup/keys/GPG-KEY-PG_PROBACKUP | sudo apt-key add - && sudo apt-get update
 sudo apt-get install pg-probackup-{13,12,11,10,9.6,9.5}
 sudo apt-get install pg-probackup-{13,12,11,10,9.6,9.5}-dbg