Fix Makefile's all target (#3085)

- Rename get_dev_tools to devtools
- tools and devtools now create a stamp after execution so
  that they are not executed twice on the same pipeline
- Add clean target to remove stamps

docs/DOCS_README.md

@@ -110,3 +110,17 @@ We are using [Algolia](https://www.algolia.com) to power full-text search. This
 Because the build processes are identical (as is the information contained herein), this file should be kept in sync as
 much as possible with its [counterpart in the Tendermint Core repo](https://github.com/tendermint/tendermint/blob/develop/docs/DOCS_README.md).
 
+### Update and Build the RPC docs
+
+1. Execute the following command at the root directory to install the swagger-ui generate tool.
+    ```
+    make tools
+    ```
+2. Edit API docs
+    1. Directly Edit API docs manually: `client/lcd/swagger-ui/swagger.yaml`.
+    2. Edit API docs within [SwaggerHub](https://app.swaggerhub.com). Please refer to this [document](https://app.swaggerhub.com/help/index) for how to use the about website to edit API docs.
+3. Download `swagger.yaml` and replace the old `swagger.yaml` under fold `client/lcd/swagger-ui`.
+4. Compile gaiacli
+    ```
+    make install
+    ```