Update prace.md PROOFREAD

line 5; I'm not sure what you mean to express at the start here. Try 'PRACE users using Anselm as they would use any other TIER - 1 ...'. Does AuP need a definition?
line 17; Try '... HOMESITE (an institution in their country) after a successful PRACE project proposal.
line 27; is it HOMESITE as in line 17 or HOMESITE as it is here? It should be consistent. In the UK, PI is Principal Investigator (I don't think it needs changing here, this is just in case you come across it an wonder)
line 37; consider 'you must' in place of 'don't forget'.
line 105; a link would be beneficial here
line 115; a link would be beneficial here
line 239; it may be beneficial to have an explanation of the difference between system and standardised core hours here (or a link to one)