(PIE-551) Docs Update

[coreymbe]

Summary

Updates to README.md to address PIE-551 and potentially PIE-351.

Detailed Description

Moved Custom Installation section to README.md. Added a paragraph to point to the Puppet Alert Actions app and repo. Additional updates made to address markdown syntax, remove harmful terminology, PE console updates, and grammatical errors.

Checklist

[ ] Draft PR?
[x] Ensure README is updated
[x] Any changes to existing documentation
[x] Anything new added
[x] Link to external Puppet documentation
[ ] Tags
[ ] Unit Tests
[ ] Acceptance Tests
[x] PR title is "(Ticket|Maint) Short Description"
[ ] Commit title matches PR title

[CLAassistant]

All committers have signed the CLA.

[Magisus]

Is there a place we could call out what error you might see -- Could not find terminus splunk_hec for indirection facts -- if your umask is set wrong?

[coreymbe]

@Magisus :: After chatting w/ Bill, there are a few things I need to tweak before this gets merged. So I should be able to find a place to add that error.

[Magisus]

I still think it would be good if we could call out the error that happens when umask is not set correctly. Otherwise the connection between the (still somewhat buried) recommendation and the error that customers are seeing is not very clear.

[coreymbe]

@bmjen @Magisus :: Sorry about that, the latest commits were to better organize the previous commits I had. Still plan to add the error to the Custom Installation section. 👍

[Magisus]

LGTM!