Fix documentation to make `yarn test` work out of the box (mk II) (#7075)

* Fix documentation to make `yarn test` work out of the box

Before, invoking `yarn test` croaked on a missing src/component-index.js
file. In another part of the README, the missing instruction to generate
this file was found.

* Fix CI: Unauthenticated git protocol on port 9418 is no longer supported

GitHub is deprecating the service which answered unauthenticated git
protocol requests. Either it happened already, or they are running
brownouts.

* This is where I meant to leave that comment

Co-authored-by: Andreas Motl <andreas.motl@panodata.org>

README.md

@@ -158,6 +158,9 @@ cd matrix-react-sdk
 git checkout develop
 yarn link matrix-js-sdk
 yarn install
+
+# Generate the `component-index.js` file.
+yarn reskindex
 ```
 
 See the [help for `yarn link`](https://classic.yarnpkg.com/docs/cli/link) for

scripts/fetchdep.sh

@@ -18,7 +18,8 @@ clone() {
     if [ -n "$branch" ]
     then
         echo "Trying to use $org/$repo#$branch"
-        git clone git://github.com/$org/$repo.git $repo --branch "$branch" --depth 1 && exit 0
+        # Disable auth prompts: https://serverfault.com/a/665959
+        GIT_TERMINAL_PROMPT=0 git clone https://github.com/$org/$repo.git $repo --branch "$branch" --depth 1 && exit 0
     fi
 }