Add NPM to distributions list

[maelstrom0x8]

This PR adds the NPM distribution of WireMock to the official documentation, specifically in the list of available distributions on the WireMock website which links to the Node.js solutions page.

Closes: wiremock/wiremock-npm#5

References

• wiremock/wiremock-npm

Submitter checklist

• [x] The PR request is well described and justified, including the body and the references
• [x] The PR title represents the desired changelog entry
• [x] If the change against WireMock 2 functionality (incompatible with WireMock 3), it is submitted against the 2.x branch
• [x] The repository's code style is followed (see the contributing guide)

Details: Contributor Guide