Add "Spaces" rule (#379)

* Proof FIXED_FIXED_CONSTANT_POOL (#207)

* docs(contributing): add "Spaces" rule

* Remove whitespace in the reference link to be consistent

CONTRIBUTING.md

@@ -68,6 +68,23 @@ R0820
  0820   LAMPTEST  CS  IMODES33
 ```
 
+### Spaces
+- Spaces between two characters in the string should respect the following convention (see the discussion in [#316][10]):
+  - Single space for new words.
+  - Double space for new sentences.
+  - Triple space for indentations.
+  
+For example the following:
+```plain
+	1)  FOO BAR BAZ QUX QUUX QUUZ. CORGE, GRAULT,
+	GARPLY, WALDO.
+```
+Should become:
+```plain
+	1) FOO BAR BAZ QUX QUUX QUUZ.  CORGE, GRAULT,
+	   GARPLY, WALDO.
+```
+
 ## Note
 
 Before you make a PR, please make sure your changes are consistent with the scans!
@@ -82,3 +99,4 @@ Before you make a PR, please make sure your changes are consistent with the scan
 [7]:https://github.com/chrislgarry/Apollo-11/issues/159
 [8]:http://www.ibiblio.org/apollo/ScansForConversion/Comanche055/
 [9]:http://www.ibiblio.org/apollo/ScansForConversion/Luminary099/
+[10]:https://github.com/chrislgarry/Apollo-11/pull/316#pullrequestreview-102892741