Create first-steps / how-to-start / first-compilation README file

[Piiit]

We need documentation for new users that want to try out the patch.

• Prerequisites for the compilation of PG
• First steps to set up a cluster, database, ...
• Connect (warn that pgAdmin may show errors)
• Examples and howtos for primitives
• Examples and howtos for temporal operators

[Piiit]

Add links to:

• Manual (LaTex) documentation
• pw_scripts on github

[Piiit]

http://www.depesz.com/2015/05/24/waiting-for-9-5-support-grouping-sets-cube-and-rollup/ could be a good example for a non-formal documentation for users.

[Piiit]

The whole syntax should be described like in a linux manpage...
In addition, it would be nice to have a changelog and version file for bigger changes and releases.