sample1d docs: small issues in desc of -A and -T

[anbj]

• grdsample -A: description of m and p; shouldn't it say "same as f", and not "same as +f" - without the plus-sign?

• If -T is set, and -A is not explicitly set, then -Af is implicitly set. -T does not mention this. I think it should.
  E.g., these two commands give the same output:

   $ gmt sample1d -T1m file
   $ gmt sample1d -T1m file -Af
  

• I can fix this, if it needs to.

[PaulWessel]

You are right. Please do.

[anbj]

Fixed in #8292.