[doc] RUM Privacy Plugin

packages/plugins/rum/src/privacy/README.md

@@ -0,0 +1,89 @@
+# RUM Privacy Plugin <!-- #omit in toc -->
+
+The RUM Privacy Plugin provides action name and session replay masking capabilities for Real User Monitoring (RUM). This plugin helps protect sensitive data while maintaining observability.
+
+## Use Cases
+
+This plugin is particularly useful for:
+- Masking sensitive data **before** sending them to Datadog
+- Providing an out-of-the-box solution with minimal instrumentation overhead 
+- Maintaining observability while ensuring privacy compliance
+
+## Reserved Global Variables
+
+The following global variable is used by this plugin:
+- `$DD_ALLOW` - Contains raw static strings from source code
+- `$DD_A_Q` - Manage the queue of adding to allowlist at runtime
+
+## File Inclusion/Exclusion for String Literal Extraction
+
+### Default Settings
+
+Excludes:
+- `node_modules` directories
+- `.preval` files
+- Files that start with special characters
+Includes:
+- files matching `/\.(?:c|m)?(?:j|t)sx?$/` 
+
+### Overrides
+You can override file inclusion/exclusion using regular expressions:
+
+```javascript
+exclude: [/packages\/apps\/mocks/]
+include: [/packages\/apps\/.*\.(?:c|m)?(?:j|t)sx?$/],
+```
+
+> Note: if you are overriding the default setting, please make sure that you are aligned with the default setting.
+
+### Excluding Code Blocks with Comments
+#### Single Line
+
+```javascript
+  "exclude line 1", // datadog-privacy-allowlist-exclude-line
+  "exclude line 2", /* datadog-privacy-allowlist-exclude-line */
+
+  /* datadog-privacy-allowlist-exclude-line */ "exclude line 3",
+
+  /*
+   datadog-privacy-allowlist-exclude-line
+   */ "exclude line 4",
+```
+
+#### Next Line
+```javascript
+  // datadog-privacy-allowlist-exclude-next-line
+  "exclude next line 1",
+
+  /* datadog-privacy-allowlist-exclude-next-line */
+  "exclude next line 2",
+
+  /*
+   datadog-privacy-allowlist-exclude-next-line
+   */
+  `exclude next line 3`,
+```
+
+#### Multi-line/Blocks
+```javascript
+  // datadog-privacy-allowlist-exclude-begin
+  "exclude range 1",
+  'exclude range 2',
+  `exclude range 3`,
+  // datadog-privacy-allowlist-exclude-end
+
+  /* datadog-privacy-allowlist-exclude-begin */
+  "exclude range with block comment 1",
+  'exclude range with block comment 2',
+  `exclude range with block comment 3`,
+  /* datadog-privacy-allowlist-exclude-end */
+
+
+  // An unterminated 'exclude-begin' should cover the rest of the file. (And extra
+  // 'exclude-begins' after that point should be ignored.)
+  /* datadog-privacy-allowlist-exclude-begin */
+  "exclude range with unterminated comment 1",
+  'exclude range with unterminated comment 2',
+  /* datadog-privacy-allowlist-exclude-begin */
+  `exclude range with unterminated comment 3`,
+```