Add changefeed in readme and update limitations (#27073)

### Packages impacted by this PR
@azure/cosmos

### Describe the problem that is addressed by this PR

- Add change feed pull model in readme.
- Update change feed limitations in readme.

### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?


### Are there test cases added in this PR? _(If not, why?)_


### Provide a list of related PRs _(if any)_


### Command used to generate this PR:**_(Applicable only to SDK release
request PRs)_

### Checklists
- [ ] Added impacted package name to the issue description
- [ ] Does this PR needs any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
repository and link it here)_
- [ ] Added a changelog (if necessary)

sdk/cosmosdb/cosmos/README.md

@@ -254,6 +254,74 @@ for (const city of resources) {
 
 For more information on querying Cosmos DB databases using the SQL API, see [Query Azure Cosmos DB data with SQL queries][cosmos_sql_queries].
 
+### Change Feed Pull Model
+
+Change feed can be fetched for a partition key, a feed range or an entire container.
+
+To process the change feed, create an instance of `ChangeFeedPullModelIterator`. When you initially create `ChangeFeedPullModelIterator`, you must specify a required `changeFeedStartFrom` value inside the `ChangeFeedIteratorOptions` which consists of both the starting position for reading changes and the resource(a partition key or a FeedRange) for which changes are to be fetched. You can optionally use `maxItemCount` in `ChangeFeedIteratorOptions` to set the maximum number of items received per page.
+
+Note: If no `changeFeedStartFrom` value is specified, then changefeed will be fetched for an entire container from Now().
+
+There are four starting positions for change feed:
+
+- `Beginning`
+
+```js
+// Signals the iterator to read changefeed from the beginning of time.
+const options = {
+  changeFeedStartFrom: ChangeFeedStartFrom.Beginning();
+}
+const iterator = container.getChangeFeedIterator(options);
+```
+
+- `Time`
+
+```js
+// Signals the iterator to read changefeed from a particular point of time.
+const time = new Date("2023/09/11") // some sample date
+const options = {
+  changeFeedStartFrom: ChangeFeedStartFrom.Time(time);
+}
+```
+
+- `Now`
+
+```js
+// Signals the iterator to read changefeed from this moment onward.
+const options = {
+  changeFeedStartFrom: ChangeFeedStartFrom.Now();
+}
+```
+
+- `Continuation`
+
+```js
+// Signals the iterator to read changefeed from a saved point.
+const continuationToken = "some continuation token recieved from previous request";
+const options = {
+  changeFeedStartFrom: ChangeFeedStartFrom.Continuation(continuationToken);
+}
+```
+
+Here's an example of fetching change feed for a partition key
+
+```js
+const partitionKey = "some-partition-Key-value";
+const options = {
+  changeFeedStartFrom: ChangeFeedStartFrom.Beginning(partitionKey),
+};
+
+const iterator = container.items.getChangeFeedIterator(options);
+
+while (iterator.hasMoreResults) {
+  const response = await iterator.readNext();
+  // process this response
+}
+```
+Because the change feed is effectively an infinite list of items that encompasses all future writes and updates, the value of `hasMoreResults` is always `true`. When you try to read the change feed and there are no new changes available, you receive a response with `NotModified` status.
+
+More detailed usage guidelines and examples of change feed can be found [here](https://learn.microsoft.com/azure/cosmos-db/nosql/change-feed-pull-model?tabs=javascript).
+
 ## Error Handling
 
 The SDK generates various types of errors that can occur during an operation.
@@ -414,9 +482,8 @@ Currently the features below are **not supported**. For alternatives options, ch
 * Aggregate cross-partition queries, like sorting, counting, and distinct, don't support continuation tokens.       Streamable queries, like SELECT \* FROM <table> WHERE <condition>, support continuation tokens. See the "Workaround" section for executing non-streamable queries without a continuation token.
 * Change Feed: Processor
 * Change Feed: Read multiple partitions key values
-* Change Feed: Read specific time
-* Change Feed: Read from the beginning
-* Change Feed: Pull model
+* Change Feed pull model all versions and delete mode [#27058](https://github.com/Azure/azure-sdk-for-js/issues/27058)
+* Change Feed pull model support for partial hierarchical partition keys [#27059](https://github.com/Azure/azure-sdk-for-js/issues/27059)
 * Cross-partition ORDER BY for mixed types
 
 ### Control Plane Limitations: