Add some how-to examples (#1905)

docs/faq-and-cookbook.rst

@@ -43,3 +43,69 @@ Capturing baggage at different contexts
 
     print(baggage.get_baggage("context", parent_ctx))
     print(baggage.get_baggage("context", child_ctx))
+
+Manually setting span context
+-----------------------------
+
+.. code-block:: python
+
+    from opentelemetry import trace
+    from opentelemetry.trace import NonRecordingSpan, SpanContext, TraceFlags
+    from opentelemetry.sdk.trace import TracerProvider
+    from opentelemetry.sdk.trace.export import ConsoleSpanExporter, SimpleSpanProcessor
+    from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator
+
+    trace.set_tracer_provider(TracerProvider())
+    trace.get_tracer_provider().add_span_processor(SimpleSpanProcessor(ConsoleSpanExporter()))
+
+    tracer = trace.get_tracer(__name__)
+
+    # Extracting from carrier header
+    carrier = {'traceparent': '00-a9c3b99a95cc045e573e163c3ac80a77-d99d251a8caecd06-01'}
+    ctx = TraceContextTextMapPropagator().extract(carrier=carrier)
+
+    with tracer.start_as_current_span('child', context=ctx) as span:
+        span.set_attribute('primes', [2, 3, 5, 7])
+
+    # Or if you have a SpanContext object already.
+    span_context = SpanContext(
+        trace_id=2604504634922341076776623263868986797,
+        span_id=5213367945872657620,
+        is_remote=True,
+        trace_flags=TraceFlags(0x01)
+    )
+    ctx = trace.set_span_in_context(NonRecordingSpan(span_context))
+
+    with tracer.start_as_current_span("child", context=ctx) as span:
+        span.set_attribute('evens', [2, 4, 6, 8])
+
+Using multiple tracer providers with different Resource
+-------------------------------------------------------
+
+.. code-block:: python
+
+    from opentelemetry import trace
+    from opentelemetry.sdk.trace import TracerProvider
+    from opentelemetry.sdk.resources import Resource
+    from opentelemetry.sdk.trace.export import ConsoleSpanExporter, SimpleSpanProcessor
+
+    # Global tracer provider which can be set only once
+    trace.set_tracer_provider(
+        TracerProvider(resource=Resource.create({"service.name": "service1"}))
+    )
+    trace.get_tracer_provider().add_span_processor(SimpleSpanProcessor(ConsoleSpanExporter()))
+
+    tracer = trace.get_tracer(__name__)
+    with tracer.start_as_current_span("some-name") as span:
+        span.set_attribute("key", "value")
+
+
+
+    another_tracer_provider = TracerProvider(
+        resource=Resource.create({"service.name": "service2"})
+    )
+    another_tracer_provider.add_span_processor(SimpleSpanProcessor(ConsoleSpanExporter()))
+
+    another_tracer = trace.get_tracer(__name__, tracer_provider=another_tracer_provider)
+    with another_tracer.start_as_current_span("name-here") as span:
+        span.set_attribute("another-key", "another-value")