Update automatic tpm installation instructions to avoid linting error

[lobis]

Currently the automatic tpm instructions are detected as syntax error by VS Code (1:1: "if <cond>" must be followed by "then"). This can be fixed by using if-shell instead (if is an alias for if-shell so behaviour should be identical, more info at https://linux.die.net/man/1/tmux).

I also added some hyperlinks to original author profiles.