help text is out of date

[ftyers]

s does not merge into supertoken https://jonorthwash.github.io/ud-annotatrix/server/public/html/help.html

[nschneid]

849b854 removes mention of s for supertoken. I suggest:

• adding a mention of s for Split, and
• rephrasing the explanation of c to Combine (instead of Merge) because it explains the mnemonic