Fix typos in the Memory and Buffers section of the docs home

[datapythonista]

Which issue does this PR close?

None

Rationale for this change

Just fixing couple of minor typos in https://docs.rs/arrow/latest/arrow/index.html#memory-and-buffers

Are there any user-facing changes?

No

[tustvold]

Thank you

[codecov-commenter]

Codecov Report

Merging #1795 (bda17b2) into master (6e6a9e1) will decrease coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1795      +/-   ##
==========================================
- Coverage   83.48%   83.38%   -0.10%     
==========================================
  Files         196      198       +2     
  Lines       55923    56205     +282     
==========================================
+ Hits        46686    46869     +183     
- Misses       9237     9336      +99     

Impacted Files	Coverage Δ
parquet/src/util/cursor.rs	62.18% <0.00%> (-1.69%)	⬇️
parquet/src/file/serialized_reader.rs	94.46% <0.00%> (-1.19%)	⬇️
parquet/src/data_type.rs	74.76% <0.00%> (-1.09%)	⬇️
parquet/src/util/bit_util.rs	93.01% <0.00%> (-1.02%)	⬇️
parquet_derive/src/parquet_field.rs	65.53% <0.00%> (-0.46%)	⬇️
arrow/src/datatypes/datatype.rs	65.42% <0.00%> (-0.38%)	⬇️
parquet/src/encodings/encoding.rs	93.46% <0.00%> (-0.20%)	⬇️
arrow/src/ipc/reader.rs	90.73% <0.00%> (-0.11%)	⬇️
arrow/src/compute/kernels/cast.rs	95.77% <0.00%> (-0.05%)	⬇️
parquet/src/file/writer.rs	92.84% <0.00%> (-0.02%)	⬇️
... and 19 more

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