add docs for patches (#2062)

reference/conanfile/tools.rst

@@ -40,3 +40,4 @@ Contents:
    tools/meson
    tools/microsoft
    tools/qbs
+   tools/files

reference/conanfile/tools/files.rst

@@ -0,0 +1,69 @@
+.. _conan_tools_files:
+
+conan.tools.files
+=================
+
+.. _conan_tools_files_patch:
+
+conan.tools.files.patch()
+-------------------------
+
+.. code-block:: python
+
+    def patch(conanfile, base_path=None, patch_file=None, patch_string=None,
+            strip=0, fuzz=False, **kwargs):
+
+Applies a diff from file (*patch_file*)  or string (*patch_string*) in *base_path* directory. If
+*base_path* is not passed it is applied in the current directory.
+
+Parameters:
+    - **base_path**: Base path where the patch should be applied.
+    - **patch_file**: Patch file that should be applied.
+    - **patch_string**: Patch string that should be applied.
+    - **strip**: Number of folders to be stripped from the path.
+    - **output**: Stream object.
+    - **fuzz**: Should accept fuzzy patches.
+    - **kwargs**: Extra parameters that can be added and will contribute to output information.
+
+.. _conan_tools_files_apply_conandata_patches:
+
+conan.tools.files.apply_conandata_patches()
+-------------------------------------------
+
+.. code-block:: python
+
+    def apply_conandata_patches(conanfile):
+
+Applies patches stored in ``conanfile.conan_data`` (read from ``conandata.yml`` file). It will apply
+all the patches under ``patches`` entry that matches the given ``conanfile.version``. If versions are
+not defined in ``conandata.yml`` it will apply all the patches directly under ``patches`` keyword.
+
+Example of ``conandata.yml`` without versions defined:
+
+.. code-block:: yaml
+
+    patches:
+    - patch_file: "patches/0001-buildflatbuffers-cmake.patch"
+      base_path: "source_subfolder"
+    - patch_file: "patches/0002-implicit-copy-constructor.patch"
+      base_path: "source_subfolder"
+      patch_type: backport
+      patch_source: https://github.com/google/flatbuffers/pull/5650
+      patch_description: Needed to build with modern clang compilers.
+
+Example of ``conandata.yml`` with different patches for different versions:
+
+.. code-block:: yaml
+
+    patches:
+      "1.11.0":
+        - patch_file: "patches/0001-buildflatbuffers-cmake.patch"
+          base_path: "source_subfolder"
+        - patch_file: "patches/0002-implicit-copy-constructor.patch"
+          base_path: "source_subfolder"
+          patch_type: backport
+          patch_source: https://github.com/google/flatbuffers/pull/5650
+          patch_description: Needed to build with modern clang compilers.
+      "1.12.0":
+        - patch_file: "patches/0001-buildflatbuffers-cmake.patch"
+          base_path: "source_subfolder"