refactor: revamp install to use fisher

[edouard-lopez]

I automated the fetching of the binary and follow fish convention for completions so we can use fisher Once it approved, we need to update the location of the plugin:

-fisher install edouard-lopez/pnpm-shell-completion
+fisher install g-plane/pnpm-shell-completion

[g-plane]

Where the fisher command comes from?

[edouard-lopez]

Fisher is the most popular plugin manager for fish ecosytem, I added a link to the repo. Also updated the source repo to install from, so it will work once merged.

[g-plane]

Considering fisher is not bulti in Fish, I think we should keep the original installation method but we can still add this new method.

[edouard-lopez]

Done