add styleguide with a few things (#1048)

STYLEGUIDE.md

@@ -0,0 +1,52 @@
+# Open OnDemand Documentation Styleguide
+
+## Headings
+
+### Titles
+
+Heading titles should capitalize every major word and lowercase
+every minor word.
+
+  * major words: Nouns, verbs (including linking verbs), adjectives, adverbs, pronouns, and all words of four letters or more are considered major words.
+
+  * minor words: Short (i.e., three letters or fewer) conjunctions, short prepositions, and all articles are considered minor words.
+
+### RST Title Underlines Characters
+
+Sphinx rst files allow for any non-alphanumeric character to be the
+title underlines. It will even allow for different pages to have different
+conventions/underline characters for different sections.
+
+Throughout this codebase title underlines are varied. However, at some point
+we should standardize to this convention which `source/customizations.rst`
+follows:
+
+* H1: ===
+* H2: ---
+* H3: ...
+* H4: ```
+* H5: TBD
+
+## Code-block spacing
+
+The convention in RST for code-block spacing is to have the content
+have 3 spaces as shown below.
+
+```raw
+  .. code-block:: sh
+
+     sudo systemctl try-restart apache2
+```
+
+This project breaks that convention by using 2 spaces in the `code-block`
+content as shown below.
+
+```raw
+  .. code-block:: sh
+
+    sudo systemctl try-restart apache2
+```
+
+While this may look more visually applealing as the content is left aligned 
+with the `code-block` text above it - text editors and IDEs show an extra space
+at this point and it's a bit off putting.