Added description paragraph.

README.md

@@ -9,7 +9,11 @@ A Rust crate providing an implementation of an RFC-compliant `EmailAddress` newt
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-TBD
+Primarily for validation, the `EmailAddress` type is constructed with `FromStr::from_str` which will raise any
+parsing errors. Prior to constructions the functions `is_valid`, `is_valid_local_part`, and `is_valid_domain` may
+also be used to test for validity without constructing an instance. This supports all of the RFC ASCII and UTF-8
+character set rules, quoted and unquoted local parts but does not yet support all of the productions required for SMTP
+headers; folding whitespace, comments, etc.
 
 ## Example
 

src/lib.rs

@@ -1,6 +1,12 @@
 /*!
 A Rust crate providing an implementation of an RFC-compliant `EmailAddress` newtype.
 
+Primarily for validation, the `EmailAddress` type is constructed with `FromStr::from_str` which will raise any
+parsing errors. Prior to constructions the functions `is_valid`, `is_valid_local_part`, and `is_valid_domain` may
+also be used to test for validity without constructing an instance. This supports all of the RFC ASCII and UTF-8
+character set rules, quoted and unquoted local parts but does not yet support all of the productions required for SMTP
+headers; folding whitespace, comments, etc.
+
 # Example
 
 The following shoes the basic `is_valid` and `from_str` functions.