Add folder content/images/ to graphicspath
- Added the folder content/images/ and placed it on \graphicspath, so that
image inclusion is simplified.
- Instead of a full relative path, if images are placed in the mentioned
folder, an \includegraphics{image-file-name} should suffice to include an
image into the file content/subject-matter.tex.
- Also updated documentation related to this, and prettified existing
documentation.