(maint) Update README styling and content

Some small updates to make the markdown more consistent with other readme type
files in this repo, as well as soms small modifications to sentences and out of
date info.

README.md

@@ -1,5 +1,4 @@
-Puppet
-======
+# Puppet
 
 [![Travis Status](https://travis-ci.com/puppetlabs/puppet.svg?branch=master)](https://travis-ci.com/puppetlabs/puppet)
 [![Appveyor Status](https://ci.appveyor.com/api/projects/status/cvhpypd4504sevqq/branch/master?svg=true)](https://ci.appveyor.com/project/puppetlabs/puppet/branch/master)
@@ -10,18 +9,16 @@ Puppet, an automated administrative engine for your Linux, Unix, and Windows sys
 administrative tasks (such as adding users, installing packages, and updating server
 configurations) based on a centralized specification.
 
-Documentation
--------------
+## Documentation
 
 Documentation for Puppet and related projects can be found online at the
 [Puppet Docs site](https://puppet.com/docs).
 
-HTTP API
---------
+### HTTP API
+
 [HTTP API Index](https://puppet.com/docs/puppet/5.5/http_api/http_api_index.html)
 
-Installation
-------------
+## Installation
 
 The best way to run Puppet is with [Puppet Enterprise (PE)](https://puppet.com/products/puppet-enterprise/),
 which also includes orchestration features, a web console, and professional support.
@@ -33,8 +30,7 @@ To install an open source release of Puppet,
 If you need to run Puppet from source as a tester or developer,
 see the [Running Puppet from Source](https://docs.puppet.com/puppet/3.8/from_source.html) guide on the docs site.
 
-Developing and Contributing
-------
+## Developing and Contributing
 
 We'd love to get contributions from you! For a quick guide to getting your
 system setup for developing, take a look at our [Quickstart
@@ -45,32 +41,29 @@ in.
 For more complete docs on developing with Puppet, take a look at the
 rest of the [developer documents](https://github.com/puppetlabs/puppet/blob/master/docs/index.md).
 
-Licensing
----------
+## Licensing
 
 See [LICENSE](https://github.com/puppetlabs/puppet/blob/master/LICENSE) file. Puppet is licensed by Puppet, Inc. under the Apache license. Puppet, Inc. can be contacted at: [email protected]
 
-Support
--------
+## Support
 
 Please log tickets and issues at our [JIRA tracker](https://tickets.puppetlabs.com).  A [mailing
 list](https://groups.google.com/forum/?fromgroups#!forum/puppet-users) is
-available for asking questions and getting help from others. In addition, there
-is an active #puppet channel on Freenode.
+available for asking questions and getting help from others.
 
 We use semantic version numbers for our releases and recommend that users stay
 as up-to-date as possible by upgrading to patch releases and minor releases as
 they become available.
 
-Bugfixes and ongoing development will occur in minor releases for the current
+Bug fixes and ongoing development will occur in minor releases for the current
 major version. Security fixes will be backported to a previous major version on
 a best-effort basis, until the previous major version is no longer maintained.
 
-For example: If a security vulnerability is discovered in Puppet 4.1.1, we
-would fix it in the 4 series, most likely as 4.1.2. Maintainers would then make
-a best effort to backport that fix onto the latest Puppet 3 release.
+For example: If a security vulnerability is discovered in Puppet 6.1.1, we
+would fix it in the 6 series, most likely as 6.1.2. Maintainers would then make
+a best effort to backport that fix onto the latest Puppet 5 release.
 
 Long-term support, including security patches and bug fixes, is available for
 commercial customers. Please see the following page for more details:
 
-[Puppet Enterprise Support Lifecycle](https://puppet.com/misc/puppet-enterprise-lifecycle)
+[Puppet Enterprise Support Lifecycle](https://puppet.com/docs/puppet-enterprise/product-support-lifecycle/)