Add description for enabling experimental features #7940

Job	Run time
Checks and variables	1m 31s
Unit Tests	1m 32s
NJS Unit Tests	35s
Build Binary	26s
Build Plus images / build	48s
Build OSS images (nginx, linux/arm64, linux/amd64) / build	46s
Build OSS images (ngf, linux/arm64, linux/amd64) / build	1m 17s
Helm Tests	0s
Functional tests (nginx, v1.25.16) / Run Tests	2m 51s
Functional tests (plus, v1.25.16) / Run Tests	2m 48s
Functional tests (nginx, v1.31.0) / Run Tests	3m 2s
Conformance tests (nginx, v1.25.16, false) / Run Tests	3m 2s
Conformance tests (nginx, v1.25.16, true) / Run Tests	3m 3s
Conformance tests (nginx, v1.31.0, false) / Run Tests	3m 1s
Functional tests (plus, v1.31.0) / Run Tests	2m 59s
Conformance tests (nginx, v1.31.0, true) / Run Tests	2m 56s
Conformance tests (plus, v1.25.16, false) / Run Tests	2m 58s
Conformance tests (plus, v1.25.16, true) / Run Tests	2m 55s
Conformance tests (plus, v1.31.0, false) / Run Tests	2m 50s
Conformance tests (plus, v1.31.0, true) / Run Tests	3m 3s
Package and Publish Helm Chart	0s
	42m 23s

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