[processor/transform] more readme refactoring (#37909)

#### Description

With the new context inference feature the user needs to know less about
the concept of an OTTL Context. This refactor restructures the README
some more to try really hard not to talk about OTTL context and instead
talk about OTTL Paths, which is the concrete thing the user needs to
know to write an OTTL statement.

#### Link to tracking issue

#29017

---------

Co-authored-by: Evan Bradley <[email protected]>
Co-authored-by: Edmo Vamerlatti Costa <[email protected]>

Author: 3 people

pkg/ottl/README.md

@@ -18,13 +18,27 @@ This package implements everything necessary to use OTTL in a Collector componen
 - [Troubleshooting](#troubleshooting)
 - [Resources](#resources)
 
+
 ## Getting Started
 
-If you're looking to write OTTL statements for a component's configuration check out these resources.
+An OTTL statement is made up of 2 parts:
+1. A function that transforms telemetry
+2. Optionally, a condition that determines whether the function is executed.
+
+Here is an example OTTL statement:
+
+```
+set(span.attributes["test"], "pass") where span.attributes["test"] == nil
+```
+
+This statement sets a new span attribute named `"test"` with a value of `"pass"` whenever the span does not already
+have an attribute named `"test"`. In this example, the **function** is `set`, which uses the second parameter to set the value of the first parameter, and the **condition** is `span.attributes["test"] == nil`.
 
-See [OTTL Functions](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/pkg/ottl/ottlfuncs#ottl-functions) for a list of functions available for use in the OTTL statements of most components.
+Within a statement you utilize OTTL Paths to access telemetry. The example uses the Path `span.attributes` to access
+the span's attributes. For each Open Telemetry Signal, OTTL has a Path to every field (plus some extras to help make
+interacting with the data easier).
 
-OTTL Contexts define how you access the fields on a given telemetry item. See the table to find the exact list of available fields:
+To see a list of available Paths for each Open Telemetry Signal, checkout the links below.
 
 | Telemetry               | OTTL Context                                                                                                                               |
 |-------------------------|--------------------------------------------------------------------------------------------------------------------------------------------|
@@ -36,7 +50,17 @@ OTTL Contexts define how you access the fields on a given telemetry item. See th
 | `Datapoint`             | [DataPoint](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/pkg/ottl/contexts/ottldatapoint/README.md)         |
 | `Log`                   | [Log](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/pkg/ottl/contexts/ottllog/README.md)                     |
 
-To understand what OTTL offers as a language, check out [OTTL's grammar doc](./LANGUAGE.md).
+OTTL does not support cross-signal interactions at this time. That means you cannot write a statement like
+
+```
+set(span.attributes["log body"], log.body)
+```
+
+See [OTTL Functions](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/pkg/ottl/ottlfuncs#ottl-functions) for a list of functions available for use in OTTL statements of most components.
+
+To see more examples of OTTL statements, checkout the [Transform Processor](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/processor/transformprocessor/README.md#examples)
+
+There is a lot more OTTL can do, like nested functions, arithmetic, indexing, and enums. To explore it further check out [OTTL's grammar doc](./LANGUAGE.md).
 
 ## Where to use OTTL