doc: Fix typos, escape [ and format table in README.md

[langbein-daniel]

👋 I did some awesome work for the Pelias project and would love for everyone to have a look at it and provide feedback.

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Here's the reason for this change 🚀

While reading through the main README of this project, I improved some formatting and fixed some typos. The content remains the same.

I escaped the first of the two [[ as some markdown readers think that e.g. [[design doc](docs/design-doc.md)] is a label. If viewed on GitHub, there is no difference, the links remain working.

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Here's how others can test the changes 👀

View the README.md file.

[missinglink]

Thanks for the PR, couple questions:

1. Why is the square bracket escaping required? it seems to render fine on Github:

2. Same for the table, it seems to be rendering fine as-is?

As seen at: https://github.com/pelias/interpolation

I also tried rendering the markdown in glow on the command line and it seems to render fine there too:

Are you having problems with a specific markdown renderer?
I'd like to know if it's a problem with the markdown encoding or the renderer, I've never had a problem with this syntax in the past.

[langbein-daniel]

I'm using the Markdown editor of a JetBrains IDE (IntelliJ).

1)

Lets look at this snippet [[design doc](docs/design-doc.md)] [[relationship to pelias](docs/introduction.md)].

My IDE checks Markdown links before each commit. While searching for links that are not inline (such as [link-text][label] and in another line [label]: http://some.url), it detected [[relationship to pelias](docs/introduction.md)] as label because just before it there is some text in square brackets [[design doc](docs/design-doc.md)].

I've double checked with CommonMark and my IDE is actually wrong in that it detects [...] [...] as non inline link. There must not be a space between the link text in [] and the label in []. See https://commonmark.org/help/tutorial/07-links.html (click on the plus for details).

So I can very gladly remove the \ again. Whereby the \, except for the readability of the source text, should have no harm.

2)

The tables are definitely fine as is. Only the readability (of the source code) is not perfect.

Markdown aims to be well readable, even in source code. Therefore I have often seen tables formatted with spaces, where the | are aligned exactly on top of each other. And so already in the editor a visually correct table results.

My IDE can "format" a Markdown table with spaces automatically, so it's not necessary to do this manually.

I just thought the formatted table might be handy for people reading the README in plain text. But I don't have a strong opinion about this. We can happily leave it as it was before as well.

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I definitely would not have opened a commit just for (1) and (2) alone. I hope now not to have generated too much effort with it ;) And I'll try to open an Issue at my IDEs Markdown plugin so that it does not detect []<SPACE>[] as label anymore.