Update remappings and install instructions for Foundry on docs site (#4498)

Co-authored-by: ernestognw <ernestognw@gmail.com>

docs/modules/ROOT/pages/index.adoc

@@ -11,11 +11,25 @@
 [[install]]
 === Installation
 
+==== Hardhat, Truffle (npm)
+
 ```console
 $ npm install @openzeppelin/contracts
 ```
 
-OpenZeppelin Contracts features a xref:releases-stability.adoc#api-stability[stable API], which means your contracts won't break unexpectedly when upgrading to a newer minor version.
+OpenZeppelin Contracts features a xref:releases-stability.adoc#api-stability[stable API], which means that your contracts won't break unexpectedly when upgrading to a newer minor version.
+
+==== Foundry (git)
+
+WARNING: When installing via git, it is a common error to use the `master` branch. This is a development branch that should be avoided in favor of tagged releases. The release process involves security measures that the `master` branch does not guarantee.
+
+WARNING: Foundry installs the latest version initially, but subsequent `forge update` commands will use the `master` branch.
+
+```console
+$ forge install OpenZeppelin/openzeppelin-contracts
+```
+
+Add `@openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/` in `remappings.txt.` 
 
 [[usage]]
 === Usage

remappings.txt

@@ -1 +1 @@
-openzeppelin/=contracts/
+@openzeppelin/contracts/=contracts/

test/governance/Governor.t.sol

@@ -3,8 +3,8 @@
 pragma solidity ^0.8.20;
 
 import {Test} from "forge-std/Test.sol";
-import {Strings} from "../../contracts/utils/Strings.sol";
+import {Strings} from "@openzeppelin/contracts/utils/Strings.sol";
-import {Governor} from "../../contracts/governance/Governor.sol";
+import {Governor} from "@openzeppelin/contracts/governance/Governor.sol";
 
 contract GovernorInternalTest is Test, Governor {
     constructor() Governor("") {}

test/metatx/ERC2771Forwarder.t.sol

@@ -3,8 +3,8 @@
 pragma solidity ^0.8.20;
 
 import {Test} from "forge-std/Test.sol";
-import {ERC2771Forwarder} from "contracts/metatx/ERC2771Forwarder.sol";
+import {ERC2771Forwarder} from "@openzeppelin/contracts/metatx/ERC2771Forwarder.sol";
-import {CallReceiverMockTrustingForwarder, CallReceiverMock} from "contracts/mocks/CallReceiverMock.sol";
+import {CallReceiverMockTrustingForwarder, CallReceiverMock} from "@openzeppelin/contracts/mocks/CallReceiverMock.sol";
 
 struct ForwardRequest {
     address from;

test/token/ERC20/extensions/ERC4626.t.sol

@@ -3,12 +3,12 @@ pragma solidity ^0.8.20;
 
 import {ERC4626Test} from "erc4626-tests/ERC4626.test.sol";
 
-import {ERC20} from "openzeppelin/token/ERC20/ERC20.sol";
+import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";
-import {ERC4626} from "openzeppelin/token/ERC20/extensions/ERC4626.sol";
+import {ERC4626} from "@openzeppelin/contracts/token/ERC20/extensions/ERC4626.sol";
 
-import {ERC20Mock} from "openzeppelin/mocks/token/ERC20Mock.sol";
+import {ERC20Mock} from "@openzeppelin/contracts/mocks/token/ERC20Mock.sol";
-import {ERC4626Mock} from "openzeppelin/mocks/token/ERC4626Mock.sol";
+import {ERC4626Mock} from "@openzeppelin/contracts/mocks/token/ERC4626Mock.sol";
-import {ERC4626OffsetMock} from "openzeppelin/mocks/token/ERC4626OffsetMock.sol";
+import {ERC4626OffsetMock} from "@openzeppelin/contracts/mocks/token/ERC4626OffsetMock.sol";
 
 contract ERC4626VaultOffsetMock is ERC4626OffsetMock {
     constructor(

test/token/ERC721/extensions/ERC721Consecutive.t.sol

@@ -4,8 +4,8 @@ pragma solidity ^0.8.20;
 
 // solhint-disable func-name-mixedcase
 
-import {ERC721} from "../../../../contracts/token/ERC721/ERC721.sol";
+import {ERC721} from "@openzeppelin/contracts/token/ERC721/ERC721.sol";
-import {ERC721Consecutive} from "../../../../contracts/token/ERC721/extensions/ERC721Consecutive.sol";
+import {ERC721Consecutive} from "@openzeppelin/contracts/token/ERC721/extensions/ERC721Consecutive.sol";
 import {Test, StdUtils} from "forge-std/Test.sol";
 
 function toSingleton(address account) pure returns (address[] memory) {

test/utils/ShortStrings.t.sol

@@ -4,7 +4,7 @@ pragma solidity ^0.8.20;
 
 import {Test} from "forge-std/Test.sol";
 
-import {ShortStrings, ShortString} from "../../contracts/utils/ShortStrings.sol";
+import {ShortStrings, ShortString} from "@openzeppelin/contracts/utils/ShortStrings.sol";
 
 contract ShortStringsTest is Test {
     string _fallback;

test/utils/math/Math.t.sol

@@ -4,7 +4,7 @@ pragma solidity ^0.8.20;
 
 import {Test} from "forge-std/Test.sol";
 
-import {Math} from "../../../contracts/utils/math/Math.sol";
+import {Math} from "@openzeppelin/contracts/utils/math/Math.sol";
 
 contract MathTest is Test {
     // CEILDIV