user-manual-intro.xml: updated bitbake -h output

The new -S syntax is in there now.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
user-manual-execution.xml: Updated "Checksum (Signatures) section.

Fixes [YOCTO #5357]

Added a paragraph at the end of this section to address the fact
that the user can now debug Bitbake's processing of signatures.
This introduces the -S bitbake option and the fact that the
user can provide a couple parameters with it: "none" and
"printdiff".

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
user-manual-execution.xml: Added how BB processes curly braces.

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>