Add support for polkadot-fellows and forks for https://weights.tasty.limo/compare?

[bkontur]

It would be cool to add:

• polkadot-fellows repo support (probably you just need to run command with new cmd params)
• comparision working between polkadot-fellows/runtimes repo and its forks

E.g. I have PR from my fork to the fellows's main with new weights: polkadot-fellows/runtimes#329 and I would like to use this web compare tool.

Or maybe another idea would be to pass: repo?=polkadot-sdk and pr=329 and the tool would comapre source and target branch.

Wdyt?

If I have some time, I can take a look and prepare PR here.