docs: documentation improvements

**Refactor and clarify the documentation in `README.md`**
- Add Highlights
- Add a Table of contents
- Clarify the way semantic-release works
- Clarify relationship with the CI environments
- Describe local install for Node projects (with a `package.json`) and global install for non-JavaScript projects
- Explain CI general configuration (environment variables and a run after all jobs are successful)
- Clarify configuration (via config file or CLI arguments)
- Clarify plugin roles and configuration
- Add doc for shareable configuration
- Add recipes
- Add resources (Videos, articles, tutorials)
- Add a Support section
- Add a Team section

**Add the following FAQs**
- How can I use a npm build script that requires the `package.json`’s version ?
- Can I use Semantic-release with Yarn?
- Can I use Semantic-release to publish non-JavaScript packages?
- Can I use Semantic-release with any CI service?
- Can I use Semantic-release with any GitLab?
- Can I use Semantic-release with any Git hosted environment?
- Can I skip the release to the npm registry?
- Can I use .npmrc options?
- How can I set the access level of the published npm package?
- Can I use Semantic-release to publish a package on Artifactory?
- Can I set the initial release version of my package to 0.0.1?
- Why does semantic-release require Node version >= 8?

**Clarify Nove 8 requirement and solutions**
- Add Node version requirement explanation and solutions
- [X] Display a link to the documentation when running on Node < 8 version

**Add recipes**
- Travis
- GitLab CI
- Travis with build stages - To be done in #573
- CircleCI workflows - To be done in #573

bin/semantic-release.js

@@ -3,22 +3,16 @@
 // Bad news: We have to write plain ES5 in this file
 // Good news: It's the only file of the entire project
 
-// eslint-disable-next-line no-var
+/* eslint-disable no-var */
+
 var semver = require('semver');
+var pkg = require('../package.json');
 
-if (semver.lt(process.version, '8.0.0')) {
+if (!semver.satisfies(process.version, pkg.engines.node)) {
   console.error(
-    `semantic-release: node version >= 8 is required. Found ${process.version}.
+    `[semantic-release]: node version ${pkg.engines.node} is required. Found ${process.version}.
 
-If there is another job running on node version >= 8, it will be picked as
-the build leader and you can safely ignore this message.
-
-If you don't have node 8 in your build matrix you can use "npx" to restore
-compatibility with minimal overhead:
-
-$ npx -p node@8 npm run semantic-release
-
-npx is bundled with npm >= 5.4, or available via npm. More info: npm.im/npx`
+See https://github.com/semantic-release/semantic-release/blob/caribou/docs/node-version.md for more details and solutions.`
   );
   process.exit(1);
 }