Add CIPD binary installation to DEPS runhooks.

bootstrap/cipd/doc/infra/tools/protoc/linux-amd64/README.md

Index: bootstrap/cipd/doc/infra/tools/protoc/linux-amd64/README.md
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+# `infra/tools/protoc/linux-amd64`
+## Building Instructions.
+
+Choose a build directory. We'll use the enviornment variable `$ROOT` to
+represent it.
+
+    $ cd $ROOT
+
+Clone the `protobuf` repository:
+
+    $ git clone https://github.com/google/protobuf
+
+Run the build. We include the following additional configuration flags:
+- `--disable-shared`: Build a static library.
+- `--prefix $ROOT/PREFIX`: The installation prefix. This allows us to install
+                           locally, so we don't need root.
+
+Build:
+
+    $ cd protobuf
+    $ ./autogen.sh
+    $ ./configure --disable-shared --prefix $ROOT/PREFIX
+    $ make -j24 install
+
+This will install the generator to `$ROOT/PREFIX`. Afterwards, strip the binary.
+This removes symbols and debugging information, including your username, from
+the binary, reducing its size from ~40MiB to ~3MiB.
+
+    $ strip -g $ROOT/PREFIX/bin/protoc
+
+We need to package the `$ROOT/PREFIX/include` directory because it includes
+the protobuf standard library. However, we don't want to include all of the
+C++ header files, nor do we want to include the compiled libraries. Prune the
+contents of `$ROOT/PREFIX` to include only:
+- The `protoc` binary.
+- The standard library header files.
+
+    $ rm -rf $ROOT/PREFIX/lib
+    $ find $ROOT/PREFIX/include -type f ! -name '*.proto' -delete
+
+Create package and deploy to `cipd` server. Tag it with the Git commit of the
+`protobuf` source from which it was built.
+
+    $ cipd create \
+      -name "infra/tools/protoc/linux-amd64" \
+      -in $ROOT/PREFIX \
+      -tag "git_commit:`git rev-parse HEAD`"