`fromAsync` - Minior doc fix [#trivial ]

[ChrisJohns-me]

Changes the documentation to make more grammatical sense + spelling fix.

[rxswiftcommunity[bot]]

	Fails
:no_entry_sign:	Danger failed to run `/app/peril-downloaded-RxSwiftCommunity/peril@org/aeryn.ts`.

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Error TypeError

api.orgs.addOrgMembership is not a function
TypeError: api.orgs.addOrgMembership is not a function
    at exports.aeryn.wrap (/app/peril-downloaded-RxSwiftCommunity/peril@org/aeryn.ts:44:24)
    at process._tickCallback (internal/process/next_tick.js:68:7)

Dangerfile

39| 
40|   try {
41|     // This throws if the user isn't a member of the org yet. If it doesn't
42|     // throw, then it means the user was already invited or has already 
43|     // accepted the invitation (we ignore the return value here).
--------------------------^
44|     await api.orgs.checkMembership({ org, username })
45|   } catch (error) {
46|     markdown(inviteMarkdown)
47|     await api.orgs.addOrgMembership({ org, username, role: "member" })

Generated by :no_entry_sign: dangerJS