[pkg/ottl] Added 'Adding new functions/converters' guidelines (open-t…

…elemetry#33117)

**Description:** 
As discussed
[here](open-telemetry#32433 (comment))
we should agree on some guidelines when it comes to creating proposals
for new functions and converters

cc @TylerHelmuth 

**Link to tracking Issue:** -

**Testing:** -

**Documentation:** -

---------

Co-authored-by: Evan Bradley <11745660+evan-bradley@users.noreply.github.com>
Co-authored-by: Tyler Helmuth <12352919+TylerHelmuth@users.noreply.github.com>
Co-authored-by: Daniel Jaglowski <jaglows3@gmail.com>

pkg/ottl/ottlfuncs/README.md

@@ -1400,3 +1400,24 @@ Functions should be named and formatted according to the following standards.
 - Functions that interact with multiple items MUST have plurality in the name. Ex: `truncate_all`, `keep_keys`, `replace_all_matches`.
 - Functions that interact with a single item MUST NOT have plurality in the name. If a function would interact with multiple items due to a condition, like `where`, it is still considered singular. Ex: `set`, `delete`, `replace_match`.
 - Functions that change a specific target MUST set the target as the first parameter.
+
+## Adding New Editors/Converters
+
+Before raising a PR with a new Editor or Converter, raise an issue to verify its acceptance. While acceptance is strongly specific to a specific use case, consider these guidelines for early assessment.
+
+Your proposal likely will be accepted if:
+- The proposed functionality is missing,
+- The proposed solution significantly improves user experience and readability for very common use cases,
+- The proposed solution is more performant in cases where it is possible to achieve the same result with existing options.
+
+It will be up for discussion if your proposal solves an issue that can be achieved in another way but does not improve user experience or performance.
+
+Your proposal likely won't be accepted if:
+- User experience is worse and assumes a highly technical user,
+- The performance of your proposal very negatively affects the processing pipeline.
+
+As with code, OTTL aims for readability first. This means:
+- Using short, meaningful, and descriptive names,
+- Ensuring naming consistency across Editors and Converters,
+- Avoiding deep nesting to achieve desired transformations,
+- Ensuring Editors and Converters have a single responsibility.