The question came to me after reading exactly this article. So I assume I have to type into the bash the command mentioned in this article after installing the Core Client.

So I first install the Core Client, then start it with ./bitcoin-qt -datadir=/what/so/ever
and then open another Linux bash cd to /usr/local/bin and type:

echo "uacomment=UASF-SegWit-BIP148" >> /what/so/ever/bitcoin.conf && bitcoin-cli stop && sleep 5 && bitcoind


But why bitcoin-cli stop && sleep 5 && bitcoind 
This doesn't make sense.

How can I check if the BIP 148 support signal was correctly set?