Minor: make it easier to find fix instructions when cargo fmt on parquet fails

[alamb]

Which issue does this PR close?

Closes #.

Rationale for this change

While working on #6840 the fmt ci check failed on parquet. For example: https://github.com/apache/arrow-rs/actions/runs/12361198145/job/34497838320

Run cargo fmt -p parquet -- --check --config skip_children=true `find . -name "*.rs" \! -name format.rs`
Diff in /__w/arrow-rs/arrow-rs/parquet/src/arrow/schema/mod.rs:1[7](https://github.com/apache/arrow-rs/actions/runs/12361198145/job/34497838320#step:7:8)75:
             Field::new("decimal256", DataType::Decimal256(39, 2), false),
         ];
         let arrow_schema = Schema::new(arrow_fields);
-        let converted_arrow_schema = ArrowSchemaConverter::new()
-            .convert(&arrow_schema)
-            .unwrap();
+        let converted_arrow_schema = ArrowSchemaConverter::new().convert(&arrow_schema).unwrap();
 
         assert_eq!(
             parquet_schema.columns().len(),
Error: Process completed with exit code 1.

However, the exact recipe to fix this was not clear (you have to run a certain command within the arquet directory)

What changes are included in this PR?

1. Add the commands needed to fix CI as comments in the script so they are visible in the failure

Example https://github.com/apache/arrow-rs/actions/runs/12361621609/job/34499177568?pr=6886

Are there any user-facing changes?

[etseidl]

🚀 Nice. Just a small correction.

[alamb]

🚀 Nice. Just a small correction.

Nice catch -- thank you

[tustvold]

Is there a reason we have such an arcane incantation?

[alamb]

Is there a reason we have such an arcane incantation?

Because for some reason cargo fmt doesn't format the files in the parquet crate.

Added in 25e1969 / #6328

[etseidl]

Is there a reason we have such an arcane incantation?

Because for some reason cargo fmt doesn't format the files in the parquet crate.

Added in 25e1969 / #6328

In particular, things like

arrow-rs/parquet/src/lib.rs

Lines 137 to 138 in 54dccad

	experimental!(mod compression);
	experimental!(mod encodings);

cause entire modules to be skipped by cargo fmt. I agree the incantation is not desirable, and was meant to be a stop-gap until a better solution can be found.

[alamb]

cause entire modules to be skipped by cargo fmt. I agree the incantation is not desirable, and was meant to be a stop-gap until a better solution can be found.

Filed #6897 to track