DOCS Theming your instance

I added a new file to explain
* where a custom theme can be created
* where themes can be downloaded
* where to add the theme on the server
* how to make the theme available on the instance
* how to set the theme as default on the instance
11 jobs for theming_your_instance in 13 minutes and 20 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #97171
build

00:03:42

 
  Test
passed #97176
analysis

00:02:47

passed #97173
federated-testing

00:04:22

passed #97175
lint

00:02:12

passed #97395
unit-testing

00:04:45

passed #97174
unit-testing-rum

00:04:52

failed #97260
unit-testing

00:04:43

failed #97172
unit-testing

00:04:58

 
  Benchmark
manual #97177
allowed to fail manual
benchmark
 
  Deploy
manual #97178
allowed to fail manual
review_app
manual #97179
allowed to fail manual
stop_review_app