docs: add note about the build matrix to the CONTRIBUTING.md docs [skip ci]
docs: add note about the build matrix to the CONTRIBUTING.md docs [skip ci]

JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl,JCMais/node-libcurl