doc/requests: stress where to POST a job description

Everett Toews asked about this on IRC.
doc/requests: group POST and GET documentation

Before, the documentation for POST and GET requests were interleaved.
doc/requests: split paragraphs into real paragraphs

The document had many long lines with single newlines here and there.
I've now separated what looks like differnet paragraphs into real
Markdown paragraphs (separated by two newlines) and rewrapped the
lines to it's easy ot see what belongs where.
doc/requests: add quotes consistently