tamer: nir: Re-define "NIR"

This was originally the "noramlized" IR, but that's not possible to do
without template expansion, which is going to happen at a later point.  So,
this is just "NIR", pronounced "near", which is an IR that is "near" to the
source code.  You can define it was "Near IR" if you want, but it's just a
homonym with a not-quite-defined acronym to me.

DEV-7145

tamer/src/nir.rs

@@ -17,17 +17,26 @@
 //  You should have received a copy of the GNU General Public License
 //  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-//! Normalized source IR.
+//! An IR that is "near" the source code.
 //!
 //! This IR is "near" the source code written by the user,
-//!   performing only normalization tasks like desugaring.
-//! The hope is that all desugaring will be done by templates in the future.
+//!   performing only basic normalization tasks like desugaring.
+//! It takes a verbose input language and translates it into a much more
+//!   concise internal representation.
+//! The hope is that most desugaring will be done by templates in the future.
+//!
+//! NIR cannot completely normalize the source input because it does not
+//!   have enough information to do so---the
+//!     template system requires a compile-time interpreter that is beyond
+//!     the capabilities of NIR,
+//!       and so a final normalization pass must be done later on in the
+//!       lowering pipeline.
 //!
 //! This is a streaming IR,
 //!   meaning that the equivalent AST is not explicitly represented as a
 //!   tree structure in memory.
 //!
-//! This IR is lossy and does not retain enough information for code
+//! NIR is lossy and does not retain enough information for code
 //!   formatting---that
 //!     type of operation will require a mapping between
 //!     XIRF and NIR,