Changes to README

[leejoow]

After re-installation on a new raspberry I ran into some issues.

I've got three remarks for the README.
When I follow it, there are two problems:

The installation of opencage gives me errors.

This package requires Rust >=1.48.0.
----------------------------------------
ERROR: Failed building wheel for cryptography

For now I have removed all opencage functionality in my local version, so it works

Furthermore, the multimon-ng package from Zanoroy has a problem in it. Capcodes are not added correctly to the messages in lots of cases. If you use the original branch from EliasOenal (https://github.com/EliasOenal/multimon-ng.git) it works.

Last remark: I am using the rtl-sdr.com dongle (https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/). This works also fine, so maybe you can add this to the readme.

[XMaarten]

pip3 install --upgrade pip
verhelpt het probleem met cryptography waarschijnlijk, ik had hetzelfde