documentation doc(routing): explain activation strategies

I would like to add the explanation Huochunpeng gave to me in this thread.

Mar 22 '20 15:03 Alfhir

Thank you for your contribution @Alfhir. Would it be possible for you to revert all the changes related purely to Markdown syntax? Those changes make this document different in style from most of the rest of the document and also obscure what the new content is. It looked like it was the addition of a single paragraph at the end only, but I wasn't sure when trying to review.

Mar 22 '20 16:03 EisenbergEffect

Sorry for the sloppy PR. It should really only change the paragraph at the end of the document (L1177+): Reusing an Existing View Model. Seems like my IDE again deleted some WS from line endings in three other places. Would you like me to change that back as well?

Mar 22 '20 18:03 Alfhir

I am not that familiar with english grammar, should it be

invoke-lifecycle means: invoke the navigation

or

invoke-lifecycle means, ...

Mar 23 '20 17:03 Alfhir

I guess invoke-lifecycle means to invoke the navigation lifecycle or invoke-lifecycle means invoking the navigation lifecycle. Normally, @EisenbergEffect will clean up new doc anyway. 😄

Mar 23 '20 21:03 3cp