[android-client][ github wiki] Standardize Documentation

[tapaswenipathak]

• Use GitHub wiki for internal to org/project documentation and move everything else to:
  1. end-user documentation
  2. developers documentation
• Do not redirect to dead mifos wiki, apache wiki, or archived repository wiki.
  1. Link to existing documentation entry points
  2. delete dups
  3. add to end-user or developer documentation.

• Add/Update documentation on upstream contribution process. Instead of having another duplicated/outdates entry point in github wiki.

-[ ] Have a docs/ directory in each repository storing less important docs specific to the project.

cc @edcable.