Added back the baggage docs

docs/src/main/asciidoc/intro.adoc

@@ -183,6 +183,48 @@ include::https://raw.githubusercontent.com/spring-cloud-samples/sleuth-documenta
 NOTE: If you're using a custom `logback-spring.xml` then you have to pass the `spring.application.name` in
 `bootstrap` instead of `application` property file. Otherwise your custom logback file won't read the property properly.
 
+==== Propagating Span Context
+
+The span context is the state that must get propagated to any child Spans across process boundaries.
+Part of the Span Context is the Baggage. The trace and span IDs are a required part of the span context.
+Baggage is an optional part.
+
+Baggage is a set of key:value pairs stored in the span context. Baggage travels together with the trace
+and is attached to every span. Spring Cloud Sleuth will understand that a header is baggage related if the HTTP
+ header is prefixed with `baggage-` and for messaging it starts with `baggage_`.
+
+IMPORTANT: There's currently no limitation of the count or size of baggage items. However, keep in mind that
+too many can decrease system throughput or increase RPC latency. In extreme cases, it could crash the app due
+to exceeding transport-level message or header capacity.
+
+Example of setting baggage on a span:
+
+[source,java]
+----
+include::{github-raw}/spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/multiple/MultipleHopsIntegrationTests.java[tags=baggage,indent=0]
+----
+
+===== Baggage vs. Span Tags
+
+Baggage travels with the trace (i.e. every child span contains the baggage of its parent). Zipkin has no knowledge of
+baggage and will not even receive that information.
+
+Tags are attached to a specific span - they are presented for that particular span only. However you
+can search by tag to find the trace, where there exists a span having the searched tag value.
+
+If you want to be able to lookup a span based on baggage, you should add corresponding entry as a tag in the root span.
+
+[source,java]
+----
+@Autowired Tracer tracer;
+
+Span span = tracer.getCurrentSpan();
+String baggageKey = "key";
+String baggageValue = "foo";
+span.setBaggageItem(baggageKey, baggageValue);
+tracer.addTag(baggageKey, baggageValue);
+----
+
 === Adding to the project
 
 ==== Only Sleuth (log correlation)
@@ -198,7 +240,7 @@ the `spring-cloud-starter-sleuth` module to your project.
               <dependency>
                   <groupId>org.springframework.cloud</groupId>
                   <artifactId>spring-cloud-dependencies</artifactId>
-                  <version>Brixton.RELEASE</version>
+                  <version>Camden.RELEASE</version>
                   <type>pom</type>
                   <scope>import</scope>
               </dependency>
@@ -219,7 +261,7 @@ the Spring BOM
 ----
 dependencyManagement { <1>
     imports {
-        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Brixton.RELEASE"
+        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Camden.RELEASE"
     }
 }
 
@@ -243,7 +285,7 @@ If you want both Sleuth and Zipkin just add the `spring-cloud-starter-zipkin` de
               <dependency>
                   <groupId>org.springframework.cloud</groupId>
                   <artifactId>spring-cloud-dependencies</artifactId>
-                  <version>Brixton.RELEASE</version>
+                  <version>Camden.RELEASE</version>
                   <type>pom</type>
                   <scope>import</scope>
               </dependency>
@@ -264,7 +306,7 @@ the Spring BOM
 ----
 dependencyManagement { <1>
     imports {
-        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Brixton.RELEASE"
+        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Camden.RELEASE"
     }
 }
 
@@ -288,7 +330,7 @@ If you want both Sleuth and Zipkin just add the `spring-cloud-sleuth-stream` dep
               <dependency>
                   <groupId>org.springframework.cloud</groupId>
                   <artifactId>spring-cloud-dependencies</artifactId>
-                  <version>Brixton.RELEASE</version>
+                  <version>Camden.RELEASE</version>
                   <type>pom</type>
                   <scope>import</scope>
               </dependency>
@@ -320,7 +362,7 @@ the Spring BOM
 ----
 dependencyManagement { <1>
     imports {
-        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Brixton.RELEASE"
+        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Camden.RELEASE"
     }
 }
 
@@ -350,7 +392,7 @@ dependency
               <dependency>
                   <groupId>org.springframework.cloud</groupId>
                   <artifactId>spring-cloud-dependencies</artifactId>
-                  <version>Brixton.RELEASE</version>
+                  <version>Camden.RELEASE</version>
                   <type>pom</type>
                   <scope>import</scope>
               </dependency>
@@ -382,7 +424,7 @@ the Spring BOM
 ----
 dependencyManagement { <1>
     imports {
-        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Brixton.RELEASE"
+        mavenBom "org.springframework.cloud:spring-cloud-dependencies:Camden.RELEASE"
     }
 }