Mention Linuxbrew as an installation method on Linux

[thedrow]

Using package managers is preferable to bootstrap scripts whenever possible.
Termius is also available through Linuxbrew so we should recommend to use that.

[codecov-io]

Codecov Report

Merging #131 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #131   +/-   ##
=======================================
  Coverage   63.43%   63.43%           
=======================================
  Files          64       64           
  Lines        2442     2442           
  Branches      229      229           
=======================================
  Hits         1549     1549           
  Misses        860      860           
  Partials       33       33

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