Align text-label wording on block placeholders

[iamthomasbishop]

Currently

When starting a new post, the first placeholder block has a text label that says Start typing or press (+) to add content.

When you add additional blocks, those text labels say Add text or type / to add content.

Proposal

Considering we don't currently provide slash commands, the second message isn't appropriate in our editor.

I propose that we show 1 consistent message – Start typing or press (+) to add content.

This is related to:
#549

[SergioEstevao]

@iamthomasbishop do you want "Start typing..." or "Start writing..." and can we keep the unicode character for now?

[iamthomasbishop]

It should probably be "writing", considering we support various input methods (voice, Pasting, etc). Good catch.

I think @koke was working on the Unicode thing, so that should be fixed soon.