Fix instrumentation library synonym (#612)

* Fix instrumentation library synonym

Address issue not resolved in #539:

https://github.com/open-telemetry/opentelemetry-specification/pull/539/files#r426546780

* Link to definition in api.md

* Link to definition from glossary.md

Co-authored-by: Armin Ruech <armin.ruech@dynatrace.com>

Author: MrAlias

specification/glossary.md

@@ -31,9 +31,11 @@ Denotes the library that provides the instrumentation for a given [Instrumented
 *Instrumented Library* and *Instrumentation Library* may be the same library
 if it has built-in OpenTelemetry instrumentation.
 
+See [Overview](overview.md#instrumentation-libraries) for a more detailed definition and naming guidelines.
+
 Example: `io.opentelemetry.contrib.mongodb`.
 
-Synonyms: *Instrumentation Library*
+Synonyms: *Instrumenting Library*
 
 <a name="name"></a>
 

specification/trace/api.md

@@ -88,8 +88,8 @@ Some applications may use multiple `TracerProvider` instances, e.g. to provide
 different settings (e.g. `SpanProcessor`s) to each of those instances and -
 in further consequence - to the `Tracer` instances created by them.
 
-- `name` (required): This name must identify the instrumentation library (e.g. `io.opentelemetry.contrib.mongodb`) and *not*
-  the instrumented library.
+- `name` (required): This name must identify the [instrumentation library](../overview.md#instrumentation-libraries)
+  (e.g. `io.opentelemetry.contrib.mongodb`) and *not* the instrumented library.
   In case an invalid name (null or empty string) is specified, a working
   default Tracer implementation as a fallback is returned rather than returning
   null or throwing an exception.