[PATCH] Update documentation to mention Pygments

[Tom Tromey <tromey@adacore.com>]

Philippe Blain pointed out that the gdb documentation does not mention
that Pygments may be used for source highlighting.  This patch updates
the docs to reflect how highlighting is actually done.
---
 gdb/doc/gdb.texinfo | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index e39f99369f4..58479ef3ed6 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -26033,10 +26033,16 @@ Show the current state of styling.
 
 @item set style sources @samp{on|off}
 Enable or disable source code styling.  This affects whether source
-code, such as the output of the @code{list} command, is styled.  Note
-that source styling only works if styling in general is enabled, and
-if @value{GDBN} was linked with the GNU Source Highlight library.  The
-default is @samp{on}.
+code, such as the output of the @code{list} command, is styled.  The
+default is @samp{on}.  Note that source styling only works if styling
+in general is enabled, and if a source highlighting library is
+available to @value{GDBN}.
+
+There are two ways that highlighting can be done.  First, if
+@value{GDBN} was linked with the GNU Source Highlight library, then it
+is used.  Otherwise, if @value{GDBN} was configured with Python
+scripting support, and if the Python Pygments package is available,
+then it will be used.
 
 @item show style sources
 Show the current state of source code styling.
-- 
2.26.3