Update README

ADD: Comments for SQLite Access Mode
ADD: Comments for SQLite Shared-Cache Mode
UPD: README
  * Add Access Mode in Connection String Table

Author: gjrtimmer

README.md

@@ -80,6 +80,7 @@ Boolean values can be one of:
 | Defer Foreign Keys | `_defer_foreign_keys` \| `_defer_fk` | `boolean` | For more information see [PRAGMA defer_foreign_keys](https://www.sqlite.org/pragma.html#pragma_defer_foreign_keys) |
 | Foreign Keys | `_foreign_keys` \| `_fk` | `boolean` | For more information see [PRAGMA foreign_keys](https://www.sqlite.org/pragma.html#pragma_foreign_keys) |
 | Ignore CHECK Constraints | `_ignore_check_constraints` | `boolean` | For more information see [PRAGMA ignore_check_constraints](https://www.sqlite.org/pragma.html#pragma_ignore_check_constraints) |
+| Mode | `mode` | <ul><li>ro</li><li>rw</li><li>rwc</li><li>memory</li></ul> | Access Mode of the database. For more information see [SQLite Open](https://www.sqlite.org/c3ref/open.html) |
 | Mutex Locking | `_mutex` | <ul><li>no</li><li>full</li></ul> | Specify mutex mode. |
 | Recursive Triggers | `_recursive_triggers` \| `_rt` | `boolean` | For more information see [PRAGMA recursive_triggers](https://www.sqlite.org/pragma.html#pragma_recursive_triggers) |
 | Shared-Cache Mode | `cache` | <ul><li>shared</li><li>private</li></ul> | Set cache mode for more information see [sqlite.org](https://www.sqlite.org/sharedcache.html) |

sqlite3.go

@@ -793,6 +793,23 @@ func errorString(err Error) string {
 //   file:test.db?cache=shared&mode=memory
 //   :memory:
 //   file::memory:
+//
+//   mode
+//     Access mode of the database.
+//     https://www.sqlite.org/c3ref/open.html
+//     Values:
+//      - ro
+//      - rw
+//      - rwc
+//      - memory
+//
+//   shared
+//     SQLite Shared-Cache Mode
+//     https://www.sqlite.org/sharedcache.html
+//     Values:
+//       - shared
+//       - private
+//
 // go-sqlite3 adds the following query parameters to those used by SQLite:
 //   _loc=XXX
 //     Specify location of time format. It's possible to specify "auto".