Repository: open-telemetry/opentelemetry-python

Issue:
Example shown in the document https://opentelemetry-python.readthedocs.io/en/stable/getting-started.html#adding-metrics doesn't work. 
**Describe your environment** Describe any aspect of your environment relevant to the problem, including your Python version, [platform](https://docs.python.org/3/library/platform.html), version numbers of installed dependencies, information about your cloud hosting provider, etc. If you're reporting a problem with a specific version of a library in this repo, please check whether the problem has been fixed on master.

I am using Python 3.8.1. Below are the details of the packages 

opentelemetry-api                      0.15b0
opentelemetry-exporter-jaeger          0.15b0
opentelemetry-instrumentation          0.15b0
opentelemetry-instrumentation-flask    0.15b0
opentelemetry-instrumentation-requests 0.15b0
opentelemetry-instrumentation-wsgi     0.15b0
opentelemetry-sdk                      0.15b0


**Steps to reproduce**
I have just copied the code for the below URL 
https://opentelemetry-python.readthedocs.io/en/stable/getting-started.html#adding-metrics

while executing it is giving me below error 

 File "metrics.py", line 19, in <module>
    requests_counter = meter.create_metric(
AttributeError: 'Meter' object has no attribute 'create_metric'

Below are few pointers to the issue 
 **Output of print(type(meter))** : <class 'opentelemetry.sdk.metrics.Meter'>

**Output of print(dir(meter))** : ['__abstractmethods__', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '__weakref__', '_abc_impl', '_collect_metrics', '_collect_observers', 'collect', 'create_counter', 'create_updowncounter', 'create_valuerecorder', 'record_batch', 'register_sumobserver', 'register_updownsumobserver', 'register_valueobserver', 'register_view', 'unregister_observer', 'unregister_view']

Basically meter doesn't have a function "create_metric". 
![image](https://user-images.githubusercontent.com/20038172/99512103-1a2b6800-29af-11eb-859b-75b2e7a7e16e.png)




I checked the functions available for the object by using dir()


Discussion:

Resolving patch:
diff --git a/docs/getting_started/metrics_example.py b/docs/getting_started/metrics_example.py
--- a/docs/getting_started/metrics_example.py
+++ b/docs/getting_started/metrics_example.py
@@ -32,7 +32,6 @@
     description="number of requests",
     unit="1",
     value_type=int,
-    label_keys=("environment",),
 )
 
 requests_counter.add(25, staging_labels)


Test patch:
diff --git a/docs/getting_started/tests/test_metrics.py b/docs/getting_started/tests/test_metrics.py
new file mode 100644
--- /dev/null
+++ b/docs/getting_started/tests/test_metrics.py
@@ -0,0 +1,29 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import os
+import subprocess
+import sys
+import unittest
+
+
+class TestBasicMetricsExample(unittest.TestCase):
+    def test_basic_meter(self):
+        dirpath = os.path.dirname(os.path.realpath(__file__))
+        test_script = "{}/../metrics_example.py".format(dirpath)
+        output = subprocess.check_output(
+            (sys.executable, test_script)
+        ).decode()
+
+        self.assertIn('name="requests"', output)
+        self.assertIn('description="number of requests"', output)