docs, readme: remove docs and add security directory (tikv#9040)

Signed-off-by: lilin90 <[email protected]>

CONTRIBUTING.md

@@ -90,8 +90,6 @@ cargo fmt
 make clippy
 ```
 
-See [Rustdoc of TiKV](https://tikv.github.io) for TiKV code documentation.
-
 See the [style doc](https://github.com/rust-lang/rfcs/blob/master/style-guide/README.md) and the [API guidelines](https://rust-lang-nursery.github.io/api-guidelines/) for details on the conventions.
 
 Please follow this style to make TiKV easy to review, maintain, and develop.
@@ -133,6 +131,8 @@ This is a rough outline of what a contributor's workflow looks like:
 - Our CI system automatically tests all pull requests.
 - Our bot will merge your PR. It can be summoned by commenting `/merge` or adding the `S: CanMerge` label (requires tests to pass and two approvals. You might have to ask your reviewer to do this).
 
+See [Rustdoc of TiKV](https://tikv.github.io) for TiKV code documentation.
+
 Thanks for your contributions!
 
 ### Finding something to work on
@@ -149,7 +149,7 @@ The TiKV team actively develops and maintains a bunch of dependencies used in Ti
 - [grpc-rs](https://github.com/tikv/grpc-rs): The gRPC library for Rust built on the gRPC C Core library and Rust Futures
 - [fail-rs](https://github.com/tikv/fail-rs): Fail points for Rust
 
-See more on [TiKV Community](https://github.com/tikv/community).
+See more in [TiKV Community](https://github.com/tikv/community).
 
 ### Format of the commit message
 

README.md

@@ -86,6 +86,7 @@ We provide multiple deployment methods, but it is recommended to use our Ansible
     You can use [`tidb-docker-compose`](https://github.com/pingcap/tidb-docker-compose/) to quickly test TiKV and TiDB on a single machine. This is the easiest way. For other ways, see [TiDB documentation](https://docs.pingcap.com/).
 
 - Try TiKV separately
+
     - [Deploy TiKV Using Docker Stack](https://tikv.org/docs/4.0/tasks/try/docker-stack/): To quickly test TiKV separately without TiDB on a single machine
     - [Deploy TiKV Using Docker](https://tikv.org/docs/4.0/tasks/deploy/docker/): To deploy a multi-node TiKV testing cluster using Docker
     - [Deploy TiKV Using Binary Files](https://tikv.org/docs/4.0/tasks/deploy/binary/): To deploy a TiKV cluster using binary files on a single node or on multiple nodes
@@ -124,13 +125,13 @@ Quick links:
 
 ### Security audit
 
-A third-party security auditing was performed by Cure53. See the full report [here](./docs/Security-Audit.pdf).
+A third-party security auditing was performed by Cure53. See the full report [here](./security/Security-Audit.pdf).
 
 ### Reporting Security Vulnerabilities
 
 To report a security vulnerability, please send an email to [TiKV-security](mailto:[email protected]) group.
 
-See [Security](./SECURITY.md) for the process and policy followed by the TiKV project.
+See [Security](./security/SECURITY.md) for the process and policy followed by the TiKV project.
 
 ## Communication