(gdb) added section on list

gdb.md

@@ -48,7 +48,7 @@ window.
 
 One can choose various layouts with the following command:
 
-```
+```gdb
 # choose layout, enable views
 layout <layout-name>
 # default layout options:
@@ -61,7 +61,7 @@ layout <layout-name>
 The `tui` command also allows to define custom layouts.
 See the example below.
 
-```
+```gdb
 # defines a layout with the name `test` and the view `regs`, `src` and `cmd`
 tui new-layout test {-horizontal regs 1 src 2} 1 cmd 1
 
@@ -69,3 +69,23 @@ tui new-layout test {-horizontal regs 1 src 2} 1 cmd 1
 tui new-layout <name>  <view> <weight> [<view> <weight>]
 tui new-layout <name> {[-horizontal] <view> <weight> [<view> <weight>]} <weight>
 ```
+
+
+### source code view
+
+The source code view - as the name suggests - displays source code.
+By default the window displays the file containing the current instruction,
+but one can choose a differnt file with the `list` command.
+Below are several examples of how to use this command.
+
+```gdb
+# when specifying a file, a line number is required
+list <file-name>:<line-number>
+
+# list knows symbol names
+list <symbol>
+list main # this will show the main function
+
+# show current execution point
+list .
+```