Add line numbers to docs

[WilliamBergamin]

Summary

This PR introduces line numbers in code block (this is present in the bolt-python docs)

BEFORE

AFTER

I like the line numbers, let me know what you think, this PR is subjective

Also adds a markdown linter config file

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #1797 (fe9fee9) into main (32d34c4) will not change coverage.
The diff coverage is n/a.

❗ Current head fe9fee9 differs from pull request most recent head d1469ed. Consider uploading reports for the commit d1469ed to get more accurate results

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  Coverage   82.27%   82.27%           
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  Files          18       18           
  Lines        1523     1523           
  Branches      441      441           
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  Hits         1253     1253           
  Misses        172      172           
  Partials       98       98           

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[misscoded]

I love the look of it, but how does it behave with regard to copy/pasting? Are the numbers carried over? If so, that'd be a no-go for me. I'd also raise this in channel just to ensure there are no unintended consequences as a result.

Barring those two things, LGTM!

[WilliamBergamin]

The numbers do not carry over 💯

Copied content

// Handle a view_submission request
app.view('view_b', async ({ ack, body, view, client, logger }) => {
  // Acknowledge the view_submission request
  await ack();

  // Do whatever you want with the input data - here we're saving it to a DB then sending the user a verification of their submission

  // Assume there's an input block with `block_1` as the block_id and `input_a`
  const val = view['state']['values']['block_1']['input_a'];
  const user = body['user']['id'];

  // Message to send user
  let msg = '';
  // Save to DB
  const results = await db.set(user.input, val);

  if (results) {
    // DB save was successful
    msg = 'Your submission was successful';
  } else {
    msg = 'There was an er

[WilliamBergamin]

I'd also raise this in channel just to ensure there are no unintended consequences as a result.

@misscoded from my post in channel seems like we have the 👍 for this PR