[gnome-calculator] help: Added basic help page for programming mode

[Robert Roth <robertroth src gnome org>]

commit 1bfca65c5650d0f34a0273dcaee352dbbf7dcf68
Author: A.M. Rowsell <amrowsell frozenelectronics ca>
Date:   Sat Oct 24 16:10:55 2020 +0000

    help: Added basic help page for programming mode
    
    Links to other articles probably need to be added, but I'm not sure
    what and where.

 help/C/mode-programming.page | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
---
diff --git a/help/C/mode-programming.page b/help/C/mode-programming.page
new file mode 100644
index 00000000..989f41be
--- /dev/null
+++ b/help/C/mode-programming.page
@@ -0,0 +1,44 @@
+<page xmlns="http://projectmallard.org/1.0/";
+      type="guide"
+      id="mode-programming">
+
+  <info>
+      <link type="guide" xref="index#number"/>
+  </info>
+
+      <title>Programming Mode</title>
+
+  <p>
+  <gui style="menuitem">Programming mode</gui> provides the tools required for common mathematical 
operations in software development. For example, programming mode makes math on hexadecimal numbers very 
easy. It also supports common boolean functions like <gui>NOT</gui>, <gui>AND</gui>, <gui>OR</gui>, etc. A 
binary view for numbers up to 64 bits long is displayed, where the user can manually toggle each bit using 
the mouse cursor.
+  </p>
+  <p>
+  Additionally, bit-shifting operations are possible by using the <gui>≪</gui> and <gui>≫</gui> buttons. 
Modulo arithmetic can be accomplished using the <gui>mod</gui> button.
+  </p>
+  <p>
+  The default word size for boolean, one's complement, and two's complement functions can be changed both in 
the <gui style="menuitem">Preferences</gui> menu, or by using the word size button in the top right of the 
keypad while in programming mode. This will affect how results from these functions are shown. For example, 
here we show the two's complement of the number 6B in 64 bit and 16 bit word sizes: 
+  </p>
+    <example>
+    <p>
+    64 bit:
+    </p>
+    <p>
+    twos 6B
+    </p>
+    <p>
+    FFFFFFFFFFFFFF95
+    </p>
+    <p>
+    16 bit:
+    </p>
+    <p>
+    twos 6B
+    </p>
+    <p>
+    FF95
+    </p>
+    </example>
+    <note style="warning">
+    <p>Attempting to enter a larger number than will fit in the selected word size will result in an 
Overflow error.</p>
+    </note>
+
+</page>