message: docs: various minor formatting changes
diff: <!--
  PLEASE HELP US PROCESS GITHUB ISSUES FASTER BY PROVIDING THE FOLLOWING INFORMATION.
  -ISSUES MISSING IMPORTANT INFORMATION MIGHT BE CLOSED WITHOUT INVESTIGATION.
  +ISSUES MISSING IMPORTANT INFORMATION MAY BE CLOSED WITHOUT INVESTIGATION.
  -->
  ## I'm submitting a...
  <!-- Check one of the following options with "x" -->
  <pre><code>
  -[ ] Regression (behavior that used to work and stopped working in a new release)
  -[ ] Bug report <!-- Please search github for a similar issue or PR before submitting -->
  +[ ] Regression (a behavior that used to work and stopped working in a new release)
  +[ ] Bug report <!-- Please search GitHub for a similar issue or PR before submitting -->
  [ ] Feature request
  [ ] Documentation issue or request
  [ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
  @@ -32,7 +32,7 @@ https://plnkr.co or similar (you can use this template as a starting point: http
  <!-- Describe the motivation or the concrete use case. -->
  -## Please tell us about your environment
  +## Environment
  <pre><code>
  Angular version: X.Y.Z
  @@ -49,7 +49,7 @@ Browser:
  - [ ] Edge version XX
  For Tooling issues:
  -- Node version: XX <!-- use `node --version` -->
  +- Node version: XX <!-- run `node --version` -->
  - Platform: <!-- Mac, Linux, Windows -->
  Others:
  