install.sh does not work on Synology DSM

[bjesuiter]

I can't use this install script to install deno on a Synology DSM Instance (with x86 processor),
since DSM on Synology does not ship with 'unzip' anymore.
Re-installing it is not trivial, since there is no package manager on DSM.

I'm currently working on a small pr to have an install script with support for 7z.

[bjesuiter]

Update: There's already a PR for this: #258
Not adding another PR from myself.