ARROW-11821: [Rust] Edit Rust README

Edits and fixes for some missing words, punctuation, and wording.

Closes apache#9576 from pierwill/docs-edit

Authored-by: pierwill <[email protected]>
Signed-off-by: Andrew Lamb <[email protected]>

rust/README.md

@@ -34,9 +34,9 @@ This part of the Arrow project is divided in 4 main components:
 
 Independently, they support a vast array of functionality for in-memory computations.
 
-Together, they allow users to write an SQL query or a `DataFrame` (using `datafusion` crate), run it against a parquet file (using `parquet` crate), evaluate it in-memory using Arrow's columnar format (using the `arrow` crate), and send to another process (using `arrow-flight` crate).
+Together, they allow users to write an SQL query or a `DataFrame` (using the `datafusion` crate), run it against a parquet file (using the `parquet` crate), evaluate it in-memory using Arrow's columnar format (using the `arrow` crate), and send to another process (using the `arrow-flight` crate).
 
-Generally speaking, the `arrow` crate offers the  functionality to develop code that uses Arrow arrays, and `datafusion` offers most operations typically found in SQL, with the notable exceptions of:
+Generally speaking, the `arrow` crate offers functionality to develop code that uses Arrow arrays, and `datafusion` offers most operations typically found in SQL, with the notable exceptions of:
 
 * `join`
 * `window` functions
@@ -48,7 +48,7 @@ There are too many features to enumerate here, but some notable mentions:
 * `DataFusion` supports `async` execution
 * `DataFusion` supports user-defined functions, aggregates, and whole execution nodes
 
-You can find more details about each crate on their respective READMEs.
+You can find more details about each crate in their respective READMEs.
 
 ## Developer's guide to Arrow Rust
 
@@ -69,7 +69,7 @@ docker run --rm -v $(pwd)/rust:/rust -it rust /bin/bash -c "cd /rust && cargo bu
 The command above assumes that are in the root directory of the project, not in the same
 directory as this README.md.
 
-You can also compile specific workspaces,
+You can also compile specific workspaces:
 
 ```bash
 cd /rust/arrow && cargo build
@@ -93,8 +93,7 @@ This populates data in two git submodules:
 - `../testing` (sourced from https://github.com/apache/arrow-testing)
 
 By default, `cargo test` will look for these directories at their
-standard location. The following Env vars can be used to override the
-location should you choose
+standard location. The following environment variables can be used to override the location:
 
 ```bash
 # Optionaly specify a different location for test data