Simplify installation instructions

README.md

build-aux/meson/postinstall.py

data/com.github.gyan000.eos-connect.appdata.png

data/com.github.hannesschulze.conecto.appdata.xml.in

data/com.github.hannesschulze.conecto.desktop.in

data/com.github.hannesschulze.conecto.gschema.xml

data/meson.build

data/test/telephony-thumbnail-source.b64

data/test/telephony-thumbnail-source2.b64

data/test/telephony-thumbnail-source3.b64

data/test/telephony-thumbnail-source4.b64

meson.build

meson/post_install.py

po/meson.build

src/meson.build