docs: simplify git cache instructions (#14562)

docs/development/build-instructions-gn.md

@@ -72,46 +72,6 @@ $ gclient sync --with_branch_heads --with_tags
 # This will take a while, go get a coffee.
 ```
 
-### Chromium git cache
-
-`depot_tools` has an option that allows the developer to set a global cache for
-all git objects of Chromium + dependencies. This option uses `git clone
---shared` to save bandwidth/space on multiple clones of the same repositories.
-
-If you intend to have several Electron build trees on the same machine (to work
-on different versions of Electron for example), it is recommended to set use
-the git cache to speed up the download of Chromium source. For example:
-
-```sh
-$ mkdir ~/.chromium-git-cache
-$ gclient config \
-    --name "src/electron" \
-    --unmanaged \
-    --cache_dir="$HOME/.chromium-git-cache" \
-    https://github.com/electron/electron
-$ gclient sync --with_branch_heads --with_tags
-```
-
-If the bootstrap script is interrupted while using the git cache, it will leave
-the cache locked. To remove the lock, pass the `--break_repo_locks` argument to
-`gclient sync`.
-
-#### Sharing the cache between multiple machines
-
-It is possible to share this directory with other machines by exporting it as
-SMB share on linux, but only one process/machine can be using the cache at a
-time. The locks created by git-cache script will try to prevent this, but it may
-not work perfectly in a network.
-
-On Windows, SMBv2 has a directory cache that will cause problems with the git
-cache script, so it is necessary to disable it by setting the registry key
-
-```sh
-HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Lanmanworkstation\Parameters\DirectoryCacheLifetime
-```
-
-to 0. More information: https://stackoverflow.com/a/9935126
-
 ## Building
 
 ```sh
@@ -224,3 +184,26 @@ the Electron binary:
 $ ./out/Default/Electron.app/Contents/MacOS/Electron electron/spec \
   --ci --enable-logging -g 'BrowserWindow module'
 ```
+
+## Sharing the git cache between multiple machines
+
+It is possible to share the gclient git cache with other machines by exporting it as
+SMB share on linux, but only one process/machine can be using the cache at a
+time. The locks created by git-cache script will try to prevent this, but it may
+not work perfectly in a network.
+
+On Windows, SMBv2 has a directory cache that will cause problems with the git
+cache script, so it is necessary to disable it by setting the registry key
+
+```sh
+HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Lanmanworkstation\Parameters\DirectoryCacheLifetime
+```
+
+to 0. More information: https://stackoverflow.com/a/9935126
+
+## Troubleshooting
+
+### Stale locks in the git cache
+If `gclient sync` is interrupted while using the git cache, it will leave
+the cache locked. To remove the lock, pass the `--break_repo_locks` argument to
+`gclient sync`.