Consolidate `main` and `master` branches into one

[boramalper]

The repo currently has two branches main and master that sound quite similar yet have distinct histories. To make the matters worse:

• install.sh in the master branch uses master
  

  feed/install.sh

  Lines 4 to 5 in 6faec2f

  	REPO="https://github.com/adsblol/feed.git"
  	BRANCH="master"

• whereas bin/adsblol-init in the main branch uses main
  

  feed/bin/adsblol-init

  Lines 45 to 46 in 2ccddf7

  	echo "[debug] creating /opt/adsblol"
  	git clone https://github.com/adsblol/feed /opt/adsblol

This is not only confusing but also a security risk as the majority of tooling will review the "main" branch by default (whether that's named main or master or something else) and sometimes only the "main" branch too.