Provide some useful information in README file, rather than punting.

Provide some useful information in README file, rather than punting.
Add some text to introduce the project to new users.

Move packaging, configuration, and compilation of OpenOCD out of
the User's Guide and into README, where it can be used by users
before configuring and compiling the documentation.

Improve notes about required Subversion repository build steps.
Add reference to the standard GNU INSTALL file.

git-svn-id: svn://svn.berlios.de/openocd/trunk@2436 b42882b7-edfa-0310-969c-e2dbd0fdcd60