Review and edit README files

[melster1010]

• Edit the READMEs for style consistency/grammar/etc
  • dandi-archive (overall readme and web app readme) dandi-archive web app readme edit dandi-archive#1386
  • dandi-cli dandi-cli readme edit dandi-cli#1170
  • dandi-hub dandi-hub readme edit dandi-hub#50
  • helpdesk dandi-helpdesk readme edit helpdesk#87
  • dandi-schema dandi-schema readme edit dandi-schema#152
• Determine and implement a common structure where applicable

[waxlamp]

@melster1010, could you please edit the description of this issue to list out which READMEs remain to edit? We can better track progress of this issue that way. Thanks!