Edit Starlark README (influxdata#7832)

plugins/processors/starlark/README.md

@@ -4,8 +4,7 @@ The `starlark` processor calls a Starlark function for each matched metric,
 allowing for custom programmatic metric processing.
 
 The Starlark language is a dialect of Python, and will be familiar to those who
-have experience with the Python language.  However, keep in mind that it is not
-Python and that there are major syntax [differences][#Python Differences].
+have experience with the Python language. However, there are major [differences](#python-differences).
 Existing Python code is unlikely to work unmodified.  The execution environment
 is sandboxed, and it is not possible to do I/O operations such as reading from
 files or sockets.
@@ -22,7 +21,7 @@ Telegraf minimum version: Telegraf 1.15.0
   ## The Starlark source can be set as a string in this configuration file, or
   ## by referencing a file containing the script.  Only one source or script
   ## should be set at once.
-  ##
+
   ## Source of the Starlark script.
   source = '''
 def apply(metric):
@@ -35,29 +34,31 @@ def apply(metric):
 
 ### Usage
 
-The script should contain a function called `apply` that takes the metric as
+The Starlark code should contain a function called `apply` that takes a metric as
 its single argument.  The function will be called with each metric, and can
 return `None`, a single metric, or a list of metrics.
+
 ```python
 def apply(metric):
 	return metric
 ```
 
-Reference the Starlark [specification][] to see the list of available types and
-functions that can be used in the script.  In addition to these the following
+For a list of available types and functions that can be used in the code, see
+the Starlark [specification][].
+
+In addition to these, the following InfluxDB-specific
 types and functions are exposed to the script.
 
-**Metric(*name*)**:
+- **Metric(*name*)**:
 Create a new metric with the given measurement name.  The metric will have no
 tags or fields and defaults to the current time.
 
 - **name**:
-The name is a [string][string] containing the metric measurement name.
+The name is a [string][] containing the metric measurement name.
 
 - **tags**:
 A [dict-like][dict] object containing the metric's tags.
 
-
 - **fields**:
 A [dict-like][dict] object containing the metric's fields.  The values may be
 of type int, float, string, or bool.
@@ -66,18 +67,20 @@ of type int, float, string, or bool.
 The timestamp of the metric as an integer in nanoseconds since the Unix
 epoch.
 
-**deepcopy(*metric*)**: Make a copy of an existing metric.
+- **deepcopy(*metric*)**: Make a copy of an existing metric.
 
 ### Python Differences
 
-While Starlark is similar to Python it is not the same.
+While Starlark is similar to Python, there are important differences to note:
 
 - Starlark has limited support for error handling and no exceptions.  If an
   error occurs the script will immediately end and Telegraf will drop the
   metric.  Check the Telegraf logfile for details about the error.
 
 - It is not possible to import other packages and the Python standard library
-  is not available.  As such, it is not possible to open files or sockets.
+  is not available.
+
+- It is not possible to open files or sockets.
 
 - These common keywords are **not supported** in the Starlark grammar:
   ```
@@ -102,6 +105,7 @@ Use `deepcopy(metric)` to create a copy of the metric.
 **How can I return multiple metrics?**
 
 You can return a list of metrics:
+
 ```python
 def apply(metric):
     m2 = deepcopy(metric)
@@ -119,6 +123,7 @@ Use the `Metric(name)` function and set at least one field.
 **What is the fastest way to iterate over tags/fields?**
 
 The fastest way to iterate is to use a for-loop on the tags or fields attribute:
+
 ```python
 def apply(metric):
     for k in metric.tags:
@@ -127,7 +132,8 @@ def apply(metric):
 ```
 
 When you use this form, it is not possible to modify the tags inside the loop,
-if this is needed you should use the `.keys()`, `.values()`, or `.items()` forms:
+if this is needed you should use one of the `.keys()`, `.values()`, or `.items()` methods:
+
 ```python
 def apply(metric):
     for k, v in metric.tags.items():