sniff: wordsmith usage text

[skip ci]

src/cmd/sniff.rs

@@ -17,8 +17,11 @@ detect other file types. It can only sniff files with the "csv", "tsv", "tab" an
 "tsv.sz", etc.) extensions.
 
 NOTE: This command "sniffs" a CSV's schema by sampling the first n rows (default: 1000)
-of a file. Its inferences are sometimes wrong if the sample is not large enough 
-(use --sample to adjust) or the file is too small to infer a pattern. 
+of a file. Its inferences are sometimes wrong if the the file is too small to infer a pattern
+or if the CSV has unusual formatting - with atypical delimiters, quotes, etc.
+
+In such cases, selectively use the --sample, --delimiter and --quote options to improve
+the accuracy of the sniffed schema.
 
 If you want more robust, guaranteed schemata, use the "schema" or "stats" commands
 instead as they scan the entire file.
@@ -59,14 +62,15 @@ sniff options:
  [default: 1000]
  --prefer-dmy Prefer to parse dates in dmy format. Otherwise, use mdy format.
  Ignored when --no-infer is enabled.
- -d, --delimiter <arg> The field delimiter for reading CSV data.
+ -d, --delimiter <arg> The delimiter for reading CSV data.
  Specify this when the delimiter is known beforehand,
  as the delimiter inferencing algorithm can sometimes fail.
  Must be a single ascii character.
  -q, --quote <arg> The quote character for reading CSV data.
  Specify this when the quote character is known beforehand,
  as the quote char inferencing algorithm can sometimes fail.
- Must be a single ascii character.
+ Must be a single ascii character - typically, double quote ("),
+ single quote ('), or backtick (`).
  --json Return results in JSON format.
  --pretty-json Return results in pretty JSON format.
  --save-urlsample <file> Save the URL sample to a file.