Improve Readme.md for not so advanced users (#1235)
Improve Readme.md for not so advanced users (#1235)

* Improve Readme.md for not so advanced users

1. Add brief description about the 3 possible ways of executing queries: passing the query to a pool, borrowing a client from a pool or obtaining an exclusive client. Give examples for the 3 of them.

2. Use the examples to teach how to reuse a pool in all of your project. This should be helpful for not so advanced users and prevents mistakes.

3. Open a troubleshooting section.

* Shrink Troubleshooting and Point to Examples

1. Troubleshooting/FAQ section will only contain a reference to the wiki FAQ. I've already moved the content to the wiki.

2. At the end of "Pooling example" point to the wiki example page. Also indicate that there they can find how to use node-postgres with promises and async/await. I've already created that content in the wiki.

cricri/node-postgres,brianc/node-postgres,brianc/node-postgres