gnucash-docs maint: Elaborate and correct the descriptions of the report price source option.

[John Ralls]

Updated	 via  https://github.com/Gnucash/gnucash-docs/commit/05227420 (commit)
	from  https://github.com/Gnucash/gnucash-docs/commit/a201379d (commit)



commit 052274207e2b565fb13c6ea8b415668b878d326d
Author: John Ralls <jralls at ceridwen.us>
Date:   Thu Aug 30 14:26:56 2018 -0700

    Elaborate and correct the descriptions of the report price source option.



Summary of changes:
 guide/C/ch_invest.xml                              |  51 +++++++++++----------
 .../C/figures/invest_stockvalue_report_options.png | Bin 57391 -> 81599 bytes
 help/C/Help_ch_Reports.xml                         |  21 +++++----
 3 files changed, 39 insertions(+), 33 deletions(-)