Add instructions for PERSIST_DIR to grist-local-testing README

[dsagal]

Context

grist-local-testing README has a how-to-use section, which didn't work.

Proposed solution

Explain in README the extra step needed to make the minimal example work.

Has this been tested?

I tested the new instruction. There are no code changes here.

• 👍 yes, I added tests to the test suite
• 💭 no, because this PR is a draft and still needs work
• 🙅 no, because this is not relevant here
• 🙋 no, because I need help

[fflorent]

Looks good to me. I made few suggestions that can be ignored.

[fflorent]

Nitpicking:

Suggested change

	Before running, create a directory where Grist will store its documents and settings:
	Before running the first time, create a directory where Grist will store its documents and settings:

[fflorent]

As an alternative, may we create the directory ourselves?

$ touch docker-compose-examples/grist-local-testing/persist/.gitkeep
$ git add -f docker-compose-examples/grist-local-testing/persist/.gitkeep # force the file to be indexed, ignoring .gitignore

And also this change to make PERSIST_DIR equal to ./persist in docker-compose.yml by default:

diff --git a/docker-compose-examples/grist-local-testing/docker-compose.yml b/docker-compose-examples/grist-local-testing/docker-compose.yml
index 028d4e0f..5ccf7399 100644
--- a/docker-compose-examples/grist-local-testing/docker-compose.yml
+++ b/docker-compose-examples/grist-local-testing/docker-compose.yml
@@ -3,6 +3,6 @@ services:
     image: gristlabs/grist:latest
     volumes:
       # Where to store persistent data, such as documents.
-      - ${PERSIST_DIR}/grist:/persist
+      - ${PERSIST_DIR:-./persist}/grist:/persist
     ports:
       - 8484:8484

What do you think?

[dsagal]

Thanks for the suggestsions, @fflorent ! I used both, and also added some hopefully-helpful instructions to the README (you can see them rendered here).

@Spoffy , what do you think?

[Spoffy]

Looks good to me, a nice usability improvement!