Update README.md

[jordaniza]

Added additional on_attach and capabilities to nvim-lspconfig

• Because this PR includes a bug fix, relevant tests have been included.
• Because this PR includes a new feature, the change was previously discussed on an Issue or with someone from the team.
• I didn't do anything of this.

---

The Language server for hardhat works great with the config in the readme, but I found a couple of features missing:

• Error diagnostics were being shown in the editor, but the keybinding to open the modal was not expanding the full error.
• Docstrings and signatures were not being loaded with

Both of these are a bit of a pain to work without, so added the recommended additional lines to the LSP config for neovim.

Let me know what you think.

[codecov-commenter]

Codecov Report

Merging #500 (3ae2b9e) into development (d85c38b) will not change coverage.
The diff coverage is n/a.

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