Add trobleshooting notes for devcontainer (#687)

.devcontainer/Dockerfile

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+FROM mcr.microsoft.com/devcontainers/anaconda:0-3
+
+# Copy environment.yml (if found) to a temp location so we update the environment. Also
+# copy "noop.txt" so the COPY instruction does not fail if no environment.yml exists.
+COPY environment.yml* .devcontainer/noop.txt /tmp/conda-tmp/
+RUN if [ -f "/tmp/conda-tmp/environment.yml" ]; then umask 0002 && /opt/conda/bin/conda env update -n base -f /tmp/conda-tmp/environment.yml; fi \
+    && rm -rf /tmp/conda-tmp
+
+# [Optional] Uncomment this section to install additional OS packages.
+# RUN apt-get update && export DEBIAN_FRONTEND=noninteractive \
+#     && apt-get -y install --no-install-recommends <your-package-list-here>

.devcontainer/README.md

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+# Devlopment with devcontainer
+This project includes a devcontainer configuration that allows you to open the project in a container with a fully configured development environment.
+Both frontend and backend environments are initialized when the container is started.
+## GitHub Codespaces
+[![Open in GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/langgenius/dify)
+
+you can simply click the button above to open this project in GitHub Codespaces.
+
+For more info, check out the [GitHub documentation](https://docs.github.com/en/free-pro-team@latest/github/developing-online-with-codespaces/creating-a-codespace#creating-a-codespace).
+
+
+## VS Code Dev Containers
+[![Open in Dev Containers](https://img.shields.io/static/v1?label=Dev%20Containers&message=Open&color=blue&logo=visualstudiocode)](https://vscode.dev/redirect?url=vscode://ms-vscode-remote.remote-containers/cloneInVolume?url=https://github.com/langgenius/dify)
+
+if you have VS Code installed, you can click the button above to open this project in VS Code Dev Containers.
+
+You can learn more in the [Dev Containers documentation](https://code.visualstudio.com/docs/devcontainers/containers).
+
+
+## Pros of Devcontainer
+Unified Development Environment: By using devcontainers, you can ensure that all developers are developing in the same environment, reducing the occurrence of "it works on my machine" type of issues.
+
+Quick Start: New developers can set up their development environment in a few simple steps, without spending a lot of time on environment configuration.
+
+Isolation: Devcontainers isolate your project from your host operating system, reducing the chance of OS updates or other application installations impacting the development environment.
+
+## Cons of Devcontainer
+Learning Curve: For developers unfamiliar with Docker and VS Code, using devcontainers may be somewhat complex.
+
+Performance Impact: While usually minimal, programs running inside a devcontainer may be slightly slower than those running directly on the host.
+
+## Troubleshooting
+if you see such error message when you open this project in codespaces:
+![Alt text](troubleshooting.png)
+
+a simple workaround is change `/signin` endpoint into another one, then login with github account and close the tab, then change it back to `/signin` endpoint. Then all things will be fine.
+The reason is `signin` endpoint is not allowed in codespaces, details can be found [here](https://github.com/orgs/community/discussions/5204)

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the
+// README at: https://github.com/devcontainers/templates/tree/main/src/anaconda
+{
+	"name": "Anaconda (Python 3)",
+	"build": { 
+		"context": "..",
+		"dockerfile": "Dockerfile"
+	},
+	"features": {
+		"ghcr.io/dhoeric/features/act:1": {},
+		"ghcr.io/devcontainers/features/node:1": {
+			"nodeGypDependencies": true,
+			"version": "lts"
+		},
+		"ghcr.io/devcontainers-contrib/features/npm-package:1": {
+			"package": "typescript",
+			"version": "latest"
+		},
+		"ghcr.io/devcontainers/features/docker-in-docker:2": {
+			"moby": true,
+			"azureDnsAutoDetection": true,
+			"installDockerBuildx": true,
+			"version": "latest",
+			"dockerDashComposeVersion": "v2"
+		}
+	},
+	"customizations": {
+		"vscode": {
+			"extensions": [
+				"ms-python.pylint",
+				"GitHub.copilot",
+				"ms-python.python"
+			]
+		}
+	},
+	"postStartCommand": "cd api && pip install -r requirements.txt",
+	"postCreateCommand": "cd web && npm install"
+
+	// Features to add to the dev container. More info: https://containers.dev/features.
+	// "features": {},
+
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	// "postCreateCommand": "python --version",
+
+	// Configure tool-specific properties.
+	// "customizations": {},
+
+	// Uncomment to connect as root instead. More info: https://aka.ms/dev-containers-non-root.
+	// "remoteUser": "root"
+}

.devcontainer/noop.txt

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+This file copied into the container along with environment.yml* from the parent
+folder. This file is included to prevents the Dockerfile COPY instruction from 
+failing if no environment.yml is found.