README.md: tone down no-frills statement

README.md: tone down no-frills statement

Features such as icons, gradients and drop-shadows were declined in the
early phases of the project to focus on designing the fundamental building
blocks well without pressure to implement additional features which may
have compromised good design decisions.

As a core team we are not against these features per se other than when
they sacrifice the ability to run well on low spec hardware, or
disproportionately increase code complexity and long term maintenance
burden.