Boatload of header cleanup

See merge request documentation/docs/installation!14

OK, so you go through a bunch of steps and come to these instructions:

> There should now be a CiviCRM link in your Drupal menu.  Click that link and
> the CiviCRM Menu, Shortcuts, Search and New Individual Blocks should appear.
> You can now explore CiviCRM end-user features and begin configuring CiviCRM
> for your site/organization needs.

This should be the end of the installation guide. But, if you skim the TOC,
it keeps on going!

I *think* what's going on here is that people wanted to add some sections
which are sort of independent of the main flow of installation.

These probably should be moved/referenced in some other way, but I don't
really want to think too hard.  This commit just mitigates the confusion
a bit by setting the subsequent sections (re:MySQL encryption and troubleshooting)
under the heading "Addenda".

When the first heading of the document says...

> "Scope of this guide and alternative installation methods"

It breaks my English parser, and I start to cry. Just a little. On the inside.

1. Use sentence-case.

2. There will have been less of the future-past-perfect.

3. Conjugate actively.

1. Use sentence-case per style-guide (all files)
2. Don't need to explain every detail in the title (WP file)

1. Title is more specific/wordy than it needs to be.

2. Capitalizing the page title ("Configuration Checklist") is correct,
   but (as a reader skimming) it *looks* wrong because it doesn't match
   the norm and it lacks anything (quotes/italics/bold) to set it aside.

Just use a plain noun instead of a proper noun.

1. Resources in redundant.
2. The other section headings have active verb-phrase. This is a little closer.
3. The dash in "Trouble-shooting" is inconsistent. It's not wrong per se, but
   it's a little unusual, and it should be consistent with the title of
   liked page.

1. Use sentence-case

2. Don't be so wordy.  The paragraph explains this stuff - you don't need
to put the whole explanation into the TOC.

Before:

* Each CMS chapter uses slightly different headings and anchors
  for the same conceptual steps.
* Several of them try to distinguish when you do/do-not need translations,
  but they're arbitrarily different.

After:

* Each CMS chapter uses the same headings and anchors.
* If there was a different anchor before, then that anchor is still valid (but it is no
  longer visible or primary).
* It still tries to distinguish when you do/do-not need translations, but
  the language is simpler and more consistent.

Add install docs for drupal 9 now that the demo site shows it works

See merge request documentation/docs/installation!8

Normalize line-endings

See merge request documentation/docs/installation!13

This repo currently has 16 markdown files, of which 8 have `CR` endings and
8 have `CR-LF` endings.  For comparison, the dev-docs and sysadmin-guide
have strictly `CR` endings.

Add info about installing sample data in drupal 8

See merge request documentation/docs/installation!11

Update docs/drupal8/index.md - small syntax fix

See merge request documentation/docs/installation!10

TLS with MySQL

See merge request documentation/docs/installation!7

Add details on allowing patching based on dependencies

See merge request documentation/docs/installation!6

Update referene from 5.21 ESR to be 5.27 ESR and bump minimum MySQL version information

See merge request documentation/docs/installation!5

Add note about pear/exception conflict resolution

See merge request documentation/docs/installation!4