Try to be more clear in README about api levels & quickstart

[ghost]

I revamped the starting out section in the README, to address the following issues:

• I tried making it super clear that the target api, minimum api & ndk version of the quickstart should be used to avoid trouble. we have so many beginners who come into the chat who use another version and don't realize this is the reason why nothing works

• the old readme mentioned recipes, and from my own years ago beginner experience this is quite confusing. recipes are an advanced tool and to a beginner it may not be clear what it is, if e.g. a recipe may be something to build their own app and they need to create one, etc

• the readme also used the word "distribution": similarly nobody knows what that is starting out, so I avoided using it and instead called it building an app, since that is what anyone coming to the project likely wants to do

• I also tried to trim the readme quick instructions down and put optional parts (e.g. the dev version) such that they stand out less, so that the non-optional steps are more obvious

Non-README fixes:

• Revamped many parts of the quickstart, including the section at the start where concepts are explained to make it more clear that usually there is no need to touch & deal with recipes, and I moved the 32-bit section of the NDK way below since it's such a special case

• The quickstart chapter in the docs recommended minimum/ndk API 19, I'm pretty sure that doesn't work. I changed it to 21 which works. It also had a mention of target API 26 although another part mentions 27. I changed it all to 27 for consistency

• The troubleshooting guide still mentions Crystax as the usual Python 3 approach, and claims the python install is inside a lib folder. Pretty sure it's always _python_bundle now, so I changed it to reflect that

[ghost]

Did some more revamping, hope you like it 😄

[inclement]

Yay documentation \o/. Looks great.

Added a couple of comments, but feel free to go ahead and merge, they don't need to be addressed here.

[inclement]

We have pythonforandroid.recommendations but don't do much with it. Maybe we should have a cli option to tell the user what versions to install for the given p4a version. Just noting that for information though, no change needed.

[inclement]

I'd be happy to just ditch this doc, I bet there are all sorts of problems users would have if they tried this, and it's so old that we don't remotely support it.

[ghost]

ok, I removed it along with another small remark about 32-bit archlinux 👍 I'm all for simplification

[AndreMiras]

Great clarifying thanks