Review and fix block hook_help text

Simplified language to make block help text clearer.

Thanks for the patch!

This patch has some problems:
- "it can also placed" ==> needs "be" in there [this is in the About section)
- I don't think I agree with the last change in the patch. It changed wording about toggling the block title display to saying 'display it' but I think the "it" is unclear. I prefer the previous wording of this paragraph. (Configuring Blocks section).

Also changing the title and parent of this issue, since it's now about fixing the help text.

There's a "the the" in the About section of this help text that also needs to be replaced with "the".

Instead of having one critical parent issue I have been asked to change the status of each child issue.

This one doesn't seem to major to me. But yes we should get it done.

This patch no longer applies. :(

So... I read through the patch again, and applied most of it (see #3). Also read through the Block help and rewrote quite a bit of it -- we don't want or need to explain the details of how to use user interfaces, we just want to give people background information and point them to the hopefully clear UI. I thought that changing the order of the Uses would eliminate some duplicate information, so I did that as well.

One other thing. The Block Content help link has to be wrapped in a check to verify that the module actually is installed. And we shouldn't have to tell people how to install a module in this help.

With all of that in mind, here's a new patch.

It's throwing error in Simplytest.me (attached screenshot error.png).

#6 patch is working fine. tested.

@manauwarsheikh : The patch is not applied on drupal core so you wont be able to check it on simplytest.me. Clone the D8 on your local and test.

The help text in the patch still needs a review, which would be greatly appreciated!

The timezone warning on simplytest.me is NOT due to this patch.

All links work and are named correctly.

The About and Use section cover all relevant issues, and are written clearly.

Docs changes are not restricted during beta. Committed 8ad9387 and pushed to 8.0.x. Thanks!