Docs: Fix various issues.

[9600]

There are various small issues which need to be fixed.

• Says "LimeSDR USB" in lots of places instead of "LimePSB RPCM", e.g. image captions and body text.
• Says "Raspberry Compute" module in various places, whereas it should be "Raspberry Pi Compute Module".
• User Guide > Board Versions. Says they should be all treated the same, but features vary. E.g. number of OCXO, FPGA for GPSDO etc. Clarify this in the text and add a simple table which lists versions vs. features (just list features which vary by board version).
• User Guide > Reference Clock. This board OCXOs not VCTCXOs (looks like LimeSDR USB copy and paste?).
• Developer Resources. This page is broken and doesn't render.