Add section on file storage

Author: Dhghomon

src/content/doc-surrealql/statements/define/bucket.mdx

@@ -22,6 +22,10 @@ PERMISSIONS @expression [ COMMENT @string ]
 
 ## Example usage
 
+A bucket backend can be set as "memory" for non-persistent in-memory storage, or as "file:/", followed by the path, for storage on disk.
+
+### Memory backend
+
 The simplest way to experiment with a bucket for files is by using the memory backend:
 
 ```surql
@@ -51,13 +55,43 @@ encoding::base64::decode("T25jZSB0aGVyZSB3ZXJlIGZvdXIgY2hpbGRyZW4gd2hvc2UgbmFtZX
 'Once there were four children whose names were Peter, Susan, Edmund, and Lucy.'
 ```
 
-If no backend is selected, the database will search for the environment variable `SURREAL_GLOBAL_BUCKET` and assign this as the global bucket. In this case, files will have a `namespace/database` prefix added (e.g. `my_global_bucket:/test_ns/test_db/somefile.txt`). A second `SURREAL_GLOBAL_BUCKET_ENFORCED` environment variable can also be used, which when set to `true` will enforce usage of the global bucket.
+### File backend
+
+A file backend can be chosen for a bucket by typing `"file:"` and then the rest of the path, if necessary.
 
 ```surql
-DEFINE BUCKET my_bucket;
+DEFINE BUCKET my_bucket BACKEND "file:/some_directory";
+DEFINE BUCKET my_bucket BACKEND "file:/some_directory";
+```
+
+A check will then be made to see if the `SURREAL_FILE_ALLOWLIST` environment variable contains the path, without which the following error will be generated.
+
+```surql
+'Bucket backend not supported: Path not allowed'
+```
+
+The following command can be used to start running an instance in which a bucket with a file backend can be defined.
+
+```bash
+# Unix
+SURREAL_FILE_ALLOWLIST="/" surreal start --user root --pass root --allow-experimental files
+
+# Windows (PowerShell)
+$env:SURREAL_FILE_ALLOWLIST = "/" 
+surreal start --user root --pass root --allow-experimental files
 ```
 
+### Global backend
+
+A global backend can also be selected, allowing all namespaces and databases access to the same file storage.
+
+If no backend is selected, the database will search for the environment variable `SURREAL_GLOBAL_BUCKET` and assign this as the global bucket. In this case, files will have a `namespace/database` prefix added (e.g. `my_global_bucket:/test_ns/test_db/somefile.txt`). A second `SURREAL_GLOBAL_BUCKET_ENFORCED` environment variable can also be used, which when set to `true` will enforce usage of the global bucket.
+
+If a global backend is set, then a `DEFINE BUCKET` statement can be as short as `DEFINE BUCKET` plus its local name, as the rest of the logic is done via environment variables.
+
 ```surql
+DEFINE BUCKET my_bucket;
+
 -- Writes to e.g. `my_global_bucket:/test_ns/test_db/my_bucket/my_book.txt`
 f"my_bucket:/my_book.txt".put("Once there were four children whose names were Peter, Susan, Edmund, and Lucy.");
 ```