Fix #592 repaired documentation cross-references

The about page and contribute basics page contained sphinx cross
references that did not point to valid files. The cross references have
been updated to point to new pages. The new cross references point to
similarily named directories to try and preserve the original intent of
the cross references.

Fix #592
Fix #592 duplicate sphinx label declaration

Fixed sphinx build error referring to declaring the same label twice.
The following error was thrown during the build process of the
projects documents:
WARNING: Duplicate explicit target name: "project proposal document"

Fix #592
Fix #592 added warning to quick-start guide

The problem that caused import errors as in #592 were caused by a pip
installation of Freeseer and a developer working with a source copy on
the same machine. This commit places a warning at the beginning of the
quick-start page that tells readers to use the developer installation
if they want to modify the source code.

Fix #592
Fix #592 fixed documentation item list

In the release-engineering page, there was a list that threw sphinx
errors when it was parsed. The output produced a list that had non-
sequential numbers. The markdown was updated to label the list
sequentially and to resolve the sphinx errors.

Fix #592